The CI120 is a small(ish) Single Board Computer based on a MIPS CPU and an SGX GPU (PowerVR), which provides GPIO, I2C, SPI, USB, ADC, and UARTs via header pins on the board. It has WiFi, Bluetooth, and also an IR receiver. There are dedicated JTAG and UART connectors.
One of the headers, which looks to have been tacked on as a bit of an afterthought, has the same layout as the Raspberry Pi 26 pin header, so many if the Pi add-on boards should be compatible.
The GPU is, as usual, driven by a closed source blob, though I have read that efforts are ongoing to open-source some or all of this. The WiFi driver also seems to need a firmware blob, so this probably applies to Bluetooth too.
https://sourcery.mentor.com/GNUToolchain/release2640 (use -EL with gcc for Little Endian code)
http://www.elinux.org/CI20_Dev_Zone has useful build information.
Source Code References
Kernel on GitHub – https://github.com/MIPS/CI20_linux (3.0.8, 3.1.16, and 3.1.18 branches, and the 3.0.8 KitKat branch).
U-Boot on GitHub, DDR config – https://github.com/MIPS/CI20_u-boot/blob/ci20-v2013.10/arch/mips/cpu/xburst/jz4780/sdram/H5TQ2G83CFR.h
RockBox have lots of links for JZ4740, most probably relevant to JZ4780 – http://www.rockbox.org/wiki/IngenicJz47xx#Jz4740
Imagination Community Learning Resources – http://community.imgtec.com/developers/mips/resources/
Secondary MIPS chips
There are two extra MIPS processors on the S0C, one in DMA and one in VPU. Both are available to program.