I'm writing the core of a system similar to Google Wave, but much simpler, more flexible, and mathematically elegant. It works peer-to-peer, too, which is nice. It's got some clever algorithms in it, and even cleverer data structures, and I've been through several iterations of the design and code. It's probably the most complex thing I've ever written, and it could be pretty darn handy in the future. This is a surprisingly difficult problem to solve well.
(I also did a quick detour one-off project: pwstore, for anybody wanting to store passwords in Haskell. I feel pretty good about this one; it's useful.)
I'm also writing a NaNoWriMo book, which I'd left half-finished back in November, because it actually was a lot of fun to write. I've got one wonderfully snarky character; if I give her first-person narrative, the story becomes extra fun. I don't even know how many words I'm up to now. It's a sprawling fantasy adventure thing.
I loved the idea of Wave, and was sad that it didn't catch on well. I'd love to hear more about your project and/or hear about it when it goes live.
Whpearson recently mentioned that people in some other online communities frequently ask "what are you working on?". I personally love asking and answering this question. I made sure to ask it at the Seattle meetup. However, I don't often see it asked here in the comments, so I will ask it:
What are you working on?
Here are some guidelines