The top-n tools I'd like to contribute open source to.

Add elastic tabstops to at least one (preferably several) mainstream editors. It can't just be an separately-downloaded plugin, the modifications have to be high-quality enough that they get included in the mainline distribution.
I don't think elastic tabstops can (or should) replace spaces or normal tabs, but I strongly believe the idea has more merit than most other people do. I think the best way to promote the idea is to put the feature in more people's hands — once they're able to experiment with it, they can more accurately judge the feature. (editors that include it as an optional feature include gedit (optional download only), Code Browser, ...)
- elastic tabstops would make proportional fonts for coding viable, something that Stroustrup agrees is good.
Help out with Perl 6, it's still got a ways to go (but also, a lot of work has already been done).
Implement an open-source version of TimeLeft. That is, it should be 1) extremely user-friendly (productivity tools sometimes paradoxically burden the user with a lot of overhead — the goal is to save them time, not waste their time), and 2) it should have roughly the same types of clocks.
Implement some of the changes to reddit that have been suggested