Several years ago I started a website called WTFormula.com Unfortunately I was the only contributor, and since I'm not a mathematician my contributions were very few. I haven't been able to convince other people with helping writing content, and eventually I dropped it for lack in interest (the domain is also available again). I still believe it would be a very useful and nice tool to have, though.

Currently I'm working on http://libflow.com (on my spare time) and I have a lot of ideas to improve it (this "rap genius for research papers" was one of the possible improvements I had in mind). Unfortunately the project is on hold because I currently don't have the money to move it to a dedicated server and enough free time to make major changes to the site.