CHDK is free enhanced firmware for your Canon Digic II based point and shoot camera. With the CHDK firmware loaded, your camera will get the following features:
- Shooting in RAW
- Live histogram (RGB, blended, luminance and for each RGB channel)
- Zebra mode (blinking highlights and shadows)
- DOF-calculator
- Battery indicator
- Scripts execution (exposure/focus/… bracketing, intervalometer and more)
- File browser
- Text reader
- Calendar
- Some fun tools and games
Currently, the CHDK firmware is available for Canon digital cameras of the following models:
- A610, Fw: 1.00D (with CHDK version for 1.00E), 1.00E, 1.00F
- A620, Fw: 1.00F ( 1.00E is not compatible. You must upgrade to 1.00F first )
- A630, Fw: 1.00C
- A640, Fw: 1.00B
- A700, Fw: 1.00B
- A710 IS, Fw: 1.00A
- S2 IS, Fw: 1.00E, 1.00F, 1.00G, 1.00I (with CHDK version for 1.00G)
- S3 IS, Fw: 1.00A
More info at How to give your low-end Canon digital camera RAW support and CHDK Wiki.

CHDK Firmware Makes Ordinary Canon Digital Cameras Run on Steroids
CHDK is free enhanced firmware for your Canon Digic II based point and shoot camera. With the CHDK firmware loaded, your camera will get the following features:
Shooting in RAW
Live histogram (RGB, blended, luminance and for each RGB channel)
Zebra…
[...] Philippines reports a serious new firmware for Canon Digic II based point and shoot [...]