Apple's photo management application, with about as many detractors as supporters.
Hints:
- Holding Alt (Option) upon launching iPhoto will prompt you to create/select a new library.
- Holding Alt (Option) + Shift upon launching will rebuild a damaged library.
- According to this piece, pressing Ctrl-Caps Lock-9 will let you use Tab to switch between extra editing features:

Resources:
- iPhotoToGoogleEarth - generates KML files for Google/Earth from geotagged images.
- Script Export - a plug-in that allows you to process iPhoto libraries for export using (any kind of) shell scripting.
- Keyword Assistant - a decent interface for inputting keywords, with auto-completion.
- iPhoto Buddy - multiple library management
- iPhoto Extractor - library recovery
- Share a library among multiple users - on the same machine (i.e., does not take into account concurrency issues on remote drives, etc., etc.)