Over the past week or so, I've been playing around with C and the z88dk (z80 development kit), and I've finally got something stable enough to run on an emulated Sinclair ZX81 +16K, which I released yesterday and can be downloaded from here - I recommend the EightyOne emulator (just search for it). If you want to see the source code, a partially commented version is posted on pastebin. Bounce is freeware, by the way.
The great thing about programming for a limited platform - and they don't come much more limited than the old ZX81 now, do they? - is that it forces you to focus on the gameplay as the graphical capabilities don't really exist, and there's no sound chip or anything fancy. So, I think I have developed a fun but simple game (with Bounce) in no time at all really, and one that would work well on a portable device, such as a smart phone or something similar, as simple games work well to relieve the boredom of travelling. As the source is in C, this makes all of the logic very portable too!
Well, what next? I think I might do a shooty thing.