diff --git a/src/calibre/customize/__init__.py b/src/calibre/customize/__init__.py
new file mode 100644
index 0000000000..140d6878ab
--- /dev/null
+++ b/src/calibre/customize/__init__.py
@@ -0,0 +1,69 @@
+from __future__ import with_statement
+__license__   = 'GPL v3'
+__copyright__ = '2008, Kovid Goyal <kovid at kovidgoyal.net>'
+
+class Plugin(object):
+    
+    #: List of platforms this plugin works on
+    #: For example: ``['windows', 'osx', 'linux']
+    supported_platforms = []
+    
+    #: The name of this plugin
+    name           = 'Trivial Plugin'
+    
+    #: The version of this plugin as a 3-tuple (major, minor, revision)
+    version        = (1, 0, 0)
+    
+    #: A short string describing what this plugin does
+    description    = _('Does absolutely nothing')
+    
+    #: The author of this plugin
+    author         = _('Unknown')
+    
+    #: When more than one plugin exists for a filetype,
+    #: the plugins are run in order of decreasing priority
+    #: i.e. plugins with higher priority will be run first.
+    #: The highest possible priority is ``sys.maxint``.
+    #: Default pririty is 1.
+    priority = 1
+    
+    #: The earliest version of calibre this plugin requires
+    minimum_calibre_version = (0, 4, 118)
+
+    def __init__(self, plugin_path):
+        '''
+        Called once when calibre plugins are initialized. Plugins are re-initialized
+        every time a new plugin is added.
+        
+        :param plugin_path: Path to the zip file this plugin is distributed in.
+        '''
+        self.plugin_path = plugin_path
+        
+    def customization_help(self):
+        '''
+        Return a string giving help on how to customize this plugin.
+        By default raise a :class:`NotImplementedError`, which indicates that
+        the plugin does not require customization. 
+        '''
+        raise NotImplementedError
+        
+    def run(self, path_to_ebook, site_customization=''):
+        '''
+        Run the plugin. Must be implemented in subclasses.
+        It should perform whatever modifications are required 
+        on the ebook and return the absolute path to the 
+        modified ebook. If no modifications are needed, it should
+        return the path to the original ebook. If an error is encountered
+        it should raise an Exception. The default implementation
+        simply return the path to the original ebook.
+        
+        :param path_to_ebook: Absolute path to the ebook
+        :param site_customization: A (possibly empty) string that the user
+                                   has specified to customize this plugin.
+                                   For example, it could be the path to a needed
+                                   executable on her system.
+                                   
+        :return: Absolute path to the modified ebook. 
+        '''
+        # Default implementation does nothing
+        return path_to_ebook 
\ No newline at end of file
diff --git a/src/calibre/customize/filetype.py b/src/calibre/customize/filetype.py
new file mode 100644
index 0000000000..765f810a89
--- /dev/null
+++ b/src/calibre/customize/filetype.py
@@ -0,0 +1,28 @@
+from __future__ import with_statement
+__license__   = 'GPL v3'
+__copyright__ = '2008, Kovid Goyal <kovid at kovidgoyal.net>'
+
+from calibre.customize import Plugin as PluginBase
+
+class Plugin(PluginBase):
+    '''
+    A plugin that is associated with a particular set of file types.
+    '''
+    
+    #: List of file types for which this plugin should be run
+    #: For example: ``['lit', 'mobi', 'prc']``
+    file_types     = []
+    
+    #: If True, this plugin is run when books are added
+    #: to the database
+    on_import      = False
+    
+    #: If True, this plugin is run whenever an any2* tool
+    #: is used, on the file passed to the any2* tool.
+    on_preprocess  = False
+    
+    #: If True, this plugin is run after an any2* tool is
+    #: used, on the final file produced by the tool.
+    on_postprocess = False
+
+    
diff --git a/src/calibre/customize/ui.py b/src/calibre/customize/ui.py
new file mode 100644
index 0000000000..22aba604b0
--- /dev/null
+++ b/src/calibre/customize/ui.py
@@ -0,0 +1,228 @@
+from __future__ import with_statement
+__license__   = 'GPL v3'
+__copyright__ = '2008, Kovid Goyal <kovid at kovidgoyal.net>'
+
+import os, shutil, traceback, functools, sys
+
+from calibre.customize import Plugin
+from calibre.customize.filetype import Plugin as FileTypePlugin
+from calibre.constants import __version__, iswindows, isosx
+from calibre.utils.config import make_config_dir, Config, ConfigProxy, \
+                                 plugin_dir, OptionParser
+
+
+version = tuple([int(x) for x in __version__.split('.')])
+
+platform = 'linux'
+if iswindows:
+    platform = 'windows'
+if isosx:
+    platform = 'osx'
+
+from zipfile import ZipFile
+
+def _config():
+    c = Config('customize')
+    c.add_opt('plugins', default={}, help=_('Installed plugins'))
+    c.add_opt('filetype_mapping', default={}, help=_('Maping for filetype plugins'))
+    c.add_opt('plugin_customization', default={}, help=_('Local plugin customization'))
+    c.add_opt('disabled_plugins', default=set([]), help=_('Disabled plugins'))
+    
+    return ConfigProxy(c)
+
+config = _config()
+
+
+class InvalidPlugin(ValueError):
+    pass
+
+def load_plugin(path_to_zip_file):
+    '''
+    Load plugin from zip file or raise InvalidPlugin error
+    
+    :return: A :class:`Plugin` instance.
+    '''
+    print 'Loading plugin from', path_to_zip_file
+    zf = ZipFile(path_to_zip_file)
+    for name in zf.namelist():
+        if name.lower().endswith('plugin.py'):
+            locals = {}
+            exec zf.read(name) in locals
+            for x in locals.values():
+                if isinstance(x, type) and issubclass(x, Plugin):
+                    if x.minimum_calibre_version > version:
+                        raise InvalidPlugin(_('%s needs calibre version at least %s')%
+                                            (x.name, x.minimum_calibre_version))
+                    if platform not in x.supported_platforms:
+                        raise InvalidPlugin(_('%s is not supported on %s')%
+                                            (x.name, platform))
+                    
+                    return x
+    raise InvalidPlugin(_('No valid plugin found in ')+path_to_zip_file)
+
+_initialized_plugins = []
+_on_import           = {}
+_on_preprocess       = {}
+_on_postprocess      = {}
+
+
+
+def reread_filetype_plugins():
+    global _on_import
+    global _on_preprocess
+    global _on_postprocess
+    _on_import           = {}
+    _on_preprocess       = {}
+    _on_postprocess      = {}
+
+    for plugin in _initialized_plugins:
+        if isinstance(plugin, FileTypePlugin):
+            for ft in plugin.file_types:
+                if plugin.on_import:
+                    if not _on_import.has_key(ft):
+                        _on_import[ft] = []
+                    _on_import[ft].append(plugin)
+                if plugin.on_preprocess:
+                    if not _on_preprocess.has_key(ft):
+                        _on_preprocess[ft] = []
+                    _on_preprocess[ft].append(plugin)
+                if plugin.on_postprocess:
+                    if not _on_postprocess.has_key(ft):
+                        _on_postprocess[ft] = []
+                    _on_postprocess[ft].append(plugin)
+                    
+                
+def _run_filetype_plugins(path_to_file, ft, occasion='preprocess'):
+    occasion = {'import':_on_import, 'preprocess':_on_preprocess, 
+                'postprocess':_on_postprocess}[occasion]
+    customization = config['plugin_customization']
+    nfp = path_to_file
+    for plugin in occasion.get(ft, []):
+        if is_disabled(plugin):
+            continue
+        sc = customization.get(plugin.name, '')
+        try:
+            nfp = plugin.run(path_to_file, sc)
+        except:
+            print 'Running file type plugin %s failed with traceback:'%plugin.name
+            traceback.print_exc()
+    return nfp
+
+run_plugins_on_import      = functools.partial(_run_filetype_plugins, 
+                                               occasion='import')
+run_plugins_on_preprocess  = functools.partial(_run_filetype_plugins, 
+                                               occasion='preprocess')
+run_plugins_on_postprocess = functools.partial(_run_filetype_plugins, 
+                                               occasion='postprocess')
+                
+
+def initialize_plugin(plugin, path_to_zip_file):
+    print 'Initializing plugin', plugin.name
+    try:
+        plugin(path_to_zip_file)
+    except Exception:
+        tb = traceback.format_exc()
+        raise InvalidPlugin((_('Initialization of plugin %s failed with traceback:')
+                            %tb) + '\n'+tb)
+    
+
+def add_plugin(path_to_zip_file):
+    make_config_dir()
+    plugin = load_plugin(path_to_zip_file)
+    initialize_plugin(plugin, path_to_zip_file)
+    plugins = config['plugins']
+    zfp = os.path.join(plugin_dir, 'name.zip')
+    if os.path.exists(zfp):
+        os.remove(zfp)
+    shutil.copyfile(path_to_zip_file, zfp)
+    plugins[plugin.name] = zfp
+    config['plugins'] = plugins
+    initialize_plugins()
+    return plugin
+
+def is_disabled(plugin):
+    return plugin.name in config['disabled_plugins']
+
+def find_plugin(name):
+    for plugin in _initialized_plugins:
+        if plugin.name == name:
+            return plugin
+
+def disable_plugin(plugin_or_name):
+    x = getattr(plugin_or_name, 'name', plugin_or_name)
+    dp = config['disabled_plugins']
+    dp.add(x)
+    config['disabled_plugins'] = dp
+
+def enable_plugin(plugin_or_name):
+    x = getattr(plugin_or_name, 'name', plugin_or_name)
+    dp = config['disabled_plugins']
+    if x in dp:
+        dp.remove(x)
+    config['disabled_plugins'] = dp
+
+def initialize_plugins():
+    global _initialized_plugins
+    _initialized_plugins = []
+    for zfp in config['plugins'].values():
+        try:
+            plugin = load_plugin(zfp)
+            initialize_plugin(plugin, zfp)
+            _initialized_plugins.append(plugin)
+        except:
+            print 'Failed to initialize plugin...'
+            traceback.print_exc()
+    _initialized_plugins.sort(cmp=lambda x,y:cmp(x.priority, y.priority), reverse=True)    
+    reread_filetype_plugins()
+    
+initialize_plugins()
+
+def option_parser():
+    parser = OptionParser(usage=_('''\
+    %prog options
+    
+    Customize calibre by loading external plugins.
+    '''))
+    parser.add_option('-a', '--add-plugin', default=None, 
+                      help=_('Add a plugin by specifying the path to the zip file containing it.'))
+    parser.add_option('--customize-plugin', default=None,
+                      help=_('Customize plugin. Specify name of plugin and customization string separated by a comma.'))
+    parser.add_option('-l', '--list-plugins', default=False, action='store_true',
+                      help=_('List all installed plugins'))
+    parser.add_option('--enable-plugin', default=None,
+                      help=_('Enable the named plugin'))
+    parser.add_option('--disable-plugin', default=None,
+                      help=_('Disable the named plugin'))
+    return parser
+
+def main(args=sys.argv):
+    parser = option_parser()
+    if len(args) < 2:
+        parser.print_help()
+        return 1
+    opts, args = parser.parse_args(args)
+    if opts.add_plugin is not None:
+        plugin = add_plugin(opts.add_plugin)
+        print 'Plugin added:', plugin.name, plugin.version
+    if opts.customize_plugin is not None:
+        name, custom = opts.customize_plugin.split(',')
+        plugin = find_plugin(name.strip())
+        if plugin is None:
+            print 'No plugin with the name %s exists'%name
+            return 1
+        config['plugin_customization'][plugin.name] = custom.strip()
+    if opts.enable_plugin is not None:
+        enable_plugin(opts.enable_plugin.strip())
+    if opts.disable_plugin is not None:
+        disable_plugin(opts.disable_plugin.strip())
+    if opts.list_plugins:
+        print 'Name\tVersion\tDisabled\tLocal Customization'
+        for plugin in _initialized_plugins:
+            print '%s\t%s\t%s\t%s'%(plugin.name, plugin.version, is_disabled(plugin), 
+                                config['plugin_customization'].get(plugin.name))
+            print '\t', plugin.customization_help()
+        
+    return 0
+    
+if __name__ == '__main__':
+    sys.exit(main())
\ No newline at end of file
diff --git a/src/calibre/debug.py b/src/calibre/debug.py
index ea21a5613d..19c2a30b42 100644
--- a/src/calibre/debug.py
+++ b/src/calibre/debug.py
@@ -21,6 +21,8 @@ Run an embedded python interpreter.
     'Module specifications are of the form full.name.of.module,path_to_module.py', default=None
     )
     parser.add_option('-c', '--command', help='Run python code.', default=None)
+    parser.add_option('-g', '--run-gui', help='Run the GUI', default=False, 
+                      action='store_true')
     parser.add_option('--migrate', action='store_true', default=False, 
                       help='Migrate old database. Needs two arguments. Path to library1.db and path to new library folder.')
     return parser
@@ -72,7 +74,10 @@ def migrate(old, new):
 
 def main(args=sys.argv):
     opts, args = option_parser().parse_args(args)
-    if opts.update_module:
+    if opts.run_gui:
+        from calibre.gui2.main import main
+        main()
+    elif opts.update_module:
         mod, path = opts.update_module.partition(',')[0], opts.update_module.partition(',')[-1]
         update_module(mod, os.path.expanduser(path))
     elif opts.command:
diff --git a/src/calibre/linux.py b/src/calibre/linux.py
index 9e8dea355c..296024c251 100644
--- a/src/calibre/linux.py
+++ b/src/calibre/linux.py
@@ -62,7 +62,8 @@ entry_points = {
                              'calibre-debug      = calibre.debug:main',
                              'calibredb          = calibre.library.cli:main',
                              'calibre-fontconfig = calibre.utils.fontconfig:main',
-                             'calibre-parallel   = calibre.parallel:main',                             
+                             'calibre-parallel   = calibre.parallel:main',
+                             'calibre-customize  = calibre.customize.ui:main',                             
                            ],
         'gui_scripts'    : [
                             __appname__+' = calibre.gui2.main:main',
diff --git a/src/calibre/utils/config.py b/src/calibre/utils/config.py
index 59db9f38e1..7f7e47b498 100644
--- a/src/calibre/utils/config.py
+++ b/src/calibre/utils/config.py
@@ -28,9 +28,11 @@ else:
     bdir = os.path.abspath(os.path.expanduser(os.environ.get('XDG_CONFIG_HOME', '~/.config')))
     config_dir = os.path.join(bdir, 'calibre')
 
+plugin_dir = os.path.join(config_dir, 'plugins')
+
 def make_config_dir():
-    if not os.path.exists(config_dir):
-        os.makedirs(config_dir, mode=448) # 0700 == 448
+    if not os.path.exists(plugin_dir):
+        os.makedirs(plugin_dir, mode=448) # 0700 == 448
 
 
 class CustomHelpFormatter(IndentedHelpFormatter):
@@ -78,6 +80,7 @@ class OptionParser(_OptionParser):
                  gui_mode=False,
                  conflict_handler='resolve',
                  **kwds):
+        usage = textwrap.dedent(usage)
         usage += '''\n\nWhenever you pass arguments to %prog that have spaces in them, '''\
                  '''enclose the arguments in quotation marks.'''
         _OptionParser.__init__(self, usage=usage, version=version, epilog=epilog,