Communication, sat's trajectory simulation.
Communication, packages of commands, re-design from standard modem communication implementation, flush memory buffer to speed up data transfer, triple flush memory with majority voting (protection from radiation damage). Visualization of calculated trajectory in simulator to generate commands for (a) ground station and (b) craft/cubesat. GPS satellites traject's simulation for proper calculation of a craft/ground station positions. Also suggested to watch perfect video about design and manufacturing of a Apollo computer (MIT). My favorite part are buttons on the front panel. Video finally made available on youtube last year. Enjoy: http://www.youtube.com/watch?v=YIBhPsyYCiM