I've been developing original games on the Raspberry Pi for the last 3 years. Here is a video of a recent game that I've released:
Its a sort of Lemmings style game, but with tools rather than assigned skills: All music and graphics are original.
The sound effects are supplied by my own sound engine partly inspired by the Commodore 64 but with 16 bit sample playback as well as waveform generation. The music is via MP3 playback recorded using whatever instruments I have to hand.
By the way. I'm doing this on RISC OS which I've been using for around 3 years too. .
The most recent product I've developed is a game writing kit. I know a few people on the RISC OS scene working on original games on the Pi.
Is anyone else writing original games on the Pi rather than emulating/porting?