Here is a brief list of science-related sites that run on the same platform as Math Overflow:

 - Science
   - [Science Stack][1]
   - [asksci.com][2]
 - Physics
   - [physics.stackexchange.com][3]
 - Electronics
   - [Electronics Exchange][4]
 - Programming
   - [Stack Overflow][5]

A complete list of these sites is available [here][6].

The one thing that I personally feel is missing is a lower-level mathematics site (a Math Underflow, if you will).  I understand the desire to keep Math Overflow relevant and interesting for professional mathematicians, but there is currently no equivalent site for amateurs and students.


  [1]: http://sciencestack.com/
  [2]: http://asksci.com/
  [3]: http://physics.stackexchange.com/
  [4]: http://electronics.stackexchange.com/
  [5]: http://stackoverflow.com/
  [6]: http://meta.stackexchange.com/questions/4/list-of-stackexchange-sites/5#5