I know I have way too many projects, but while I was waiting for my violin lesson yesterday, I started working on a 3-D graphing program - in TI-BASIC for my Ti-84+ Silver Edition. Right now, it actually can graph simple equations (I didn't feel like making a complicated expression parser). I know there's already a 3-D graphing program in assembly by Detached Solutions, but this is just something to occupy my spare time when I have a calculator with me, but not a computer. Who knows, maybe it'll actually turn out kind of useful. For now, though, it's just kind of a neat TI-BASIC program.
I'll try to get some screenshots up.