- Quicksilver an application launcher and command runner has changed the way I interact with my Mac.
- Delicious Library winner of Apple Design Award 2005 Best Design Experience, create a catalog of all your books, DVDs, CDs and video games
- Audio Hijack lets you directly record the audio output of any other application. I like to capture the RealPlayer streams from NPR stories.
- SSH Tunnel Manager lets you easily manage SSH tunnels without having to open a window for each server you're connected to
- SubEthaEdit a great general purpose text editor that allows multiple people to edit a document in realtime
- Inquisitor adds Google Suggest-like functionality to the Safari search box
- Paparazzi! makes screenshot of web pages
Most of these are shareware or freeware, not Free software (sorry Sean) which is a really exciting part of the Mac software community. The UI quality of these apps are generally much higher than Free software and licenses are cheap and permissive.
