https://github.com/raspberrypi
1. firmware
https://github.com/raspberrypi/firmware
firmware and opt/vc from original debian sdcard release
2. quake3
https://github.com/raspberrypi/quake3
a baseline Quake 3 which may be used for further development.
3. linux
https://github.com/raspberrypi/linux
kernel source
4. tools
https://github.com/raspberrypi/tools
toolchain and tool to produce kernel.img
5. initial patches
http://elinux.org/images/8/8a/Rpi-linux-patches-3.1.9.tgz
http://elinux.org/RPi_Software#Kernel
Kernel
The initial patches (Media:Rpi-linux-patches-3.1.9.tgz) are released against the 3.1.9 kernel - but may also work against later kernels.The kernel is now also available on https://github.com/raspberrypi/linux
6. bcm2708
http://www.cnx-software.com/2012/01/22/linux-kernel-3-1-9-for-raspberry-pi-released
[..]
The code related to Broadcom BCM2835 processor is referred as bcm2708 in the kernel and I can see committed related to the watchdog timer, the framebuffer, the VCHIQ driver (the driver sending messages to the GPU) and general commits for bcm2708.
For those interested in the messages used to communicate between userspace and the GPU, the VCHIQ driver code is located at drivers/misc/vc04_services in the tree. I haven't studied it yet, but as the platform should support graphics standards such as OpenGL and OpenMAX IL, most people should not really care about this interface as I suppose the OpenGL library (Mesa?) uses this driver.
