Alright, a few ideas of mine though are really just about learning things for me. Here's one though that I really wanted to work on, but got bogged down in exactly how to go about doing it.

I started work on a fully extensible browser. My idea was to create a bare minimum browser, then extend that with plugins created in a scripting language like LUA. The browser would only run with the plugins the user selected, so someone could use a browser that only had features they wanted and used. This was also in response to perceived bloat in current modern browsers. This was a rather large undertaking, and it never got beyond a simple browser with basic cookie management.