CHDK is a firmware enhancement for many digital point and shoot cameras made by Canon. After loading CHDK, you get access to a ton of features your PowerShot normally wouldn't have.
- Enhanced ways of recording images: RAW, JPEG, increased video recording times, different compression options
- Information Displays: live histograms, always on battery life indicator, depth of focus
- Photographic Settings: longer exposure times (up to 65 seconds), faster shutter speeds (1/25,000 sec, and faster in some cases), automatic bracketing of exposure
- Scripts: programmable through scripting for creating new features (i.e. trigger shot when movement sensed, change in brightness, automatic bracketing, games)
- Tethered Shooting
The possibilities are seemingly endless. This is definitely a great hack and most importantly, it's non destructive to your camera. You aren't ever replacing the original firmware—just loading more things into memory on demand.