I was previously thinking of making a game where 2 players controlled two objects (with 2 sets of keys on a single calc). This meant that the program must handle the possibility of multiple keys being pressed at the same time. Has something like this been done before?
I imagine you could do it is asm. It could be interesting if you do figure it out. I've had several times I've wanted to do that.
I believe there are at least 2 or 3 ASM programs or Flash apps that allow you to detect simultaneous keypresses. xLIB allows you to detect simultaneous arrow keys—like Up + Right, or Down + Right. xLIB is pretty big, though, and it may be a little much to ask your user to install xLIB to play your game. Another option is the ASM program XKeys. That's all I can think of off-hand, but I believe there's some more, if you'd search around the ticalc.org archive.
I use xkeys too. I just wish it could handle lists.