A few days ago I stumbled across a Mac OS X Leopard-only prefpane that utilizes the mach-inject bundle to replace the useful (but inevitably to soon be disabled by Apple) InputManager SIMBL. The prefpane is called PlugSuit and runs the same plugins that SIMBL does, but at the user level, not the root level, as well as providing you with a useful System Preferences interface for activating and deactivating single plugins and for creating an Exclude list for applications that you don’t want to ever load plugins (like all the applications in /System/Library/CoreServices that are the base of Mac OS X). I’ve installed 5 plugins so far that run “under the hood” of OS X. Those are FlickrBooth, Avatars, SafariStand, Scalp, and Afloat.
FlickrBooth simply adds upload abilities to PhotoBooth for images uploading to Flickr and movies uploading to YouTube. It lets you set the default metadata and can even prompt for upload right after the picture or movie is taken or (though this seems dangerous unless for a security spy script) automatically upload the movies or pictures.
Avatars improves upon Address Book to let you download peoples Gravatars, Pavatars, or hCard images for use in their contact card on your Mac.
SafariStand adds a TON of useful features to Safari. They are things like download folder organization by date, automatic finding when you start typing outside of a text field, enhanced tab features, and many more that I haven’t yet explored.
Scalp gives iCal the ability to publish calendars via FTP and SFTP. It works in the background (no extra interface elements), but is a powerful enhancement to iCal.
Afloat adds a couple of powerful menu items to the Window menu of every application (that the plugin is allowed to load in, none that are in your Exclude list). These include keeping windows above all others (but as a preference letting clicks fall through), transparency options (including the window being transparent unless the mouse is over it), overlay controls, and many others accessible from a panel that you have access to from a menu item (including the window being in every space, OS X only gives you that choice for applications.
Each plugin is very useful to me and probably would be to some of you as well. Just be careful, most of the installers will install SIMBL as well, that you need to remove to allow PlugSuit to use the plugin (SIMBL gets installed in either /Library/InputManagers or ~/Libarary/InputManagers (plus these are all hacks, use at your own risk!!). Enjoy, Alex.