Whilst a lot of my build was with bits bought from part runs on the forums, I wanted to do the main control system for R2 myself. Being a Linux sysadmin for a number of years, and having used Linux since about 1994, I decided to use a Raspberry Pi. From this, R2 Control was born.
The Pi will be a wireless access point for its own private network, which makes the options for controlling the droid extremely wide.
R2 Control interfaces with all the hardware in R2, and provides a REST API to access it. This means that the actual controls can be just about anything from another program that makes the API calls, to a remote module on the network.
Currently supported hardware: https://github.com/dpoulson/r2_control/wiki/Hardware-Support
Current control options: https://github.com/dpoulson/r2_control/wiki/Controllers
Check out the github project for more details: https://github.com/dpoulson/r2_control
If you want to give this control system a try, feel free to give me a shout and we can discuss if its suitable, etc. Its all totally free to use, but the documentation is definitely a work in progress, and the code is very actively being developed.