- Writing a MIDI player on ARM. Not this fancy Android thing, it was for a simple (and old today) ARM board,, no OS and I think 64k of RAM (or maybe 512k, not sure). Doing the audio synth and everything. (this was for a univ. project), it wasn't great, sure, but it did the trick

- How to store data in an embedded Linux system with no writable partitions. (That's more of a hack than everything, still, it worked!)