Project Euler

Project Euler
http://projecteuler.net/

Project Euler is a set of mathematical or computer science-related problems. It doesn't matter how you get the answer, as the inputs are given. Users are ranked not purely by how many problems they solved, but each problem is given a score - how much it's worth - depending how many users solved it.

The site is an upgrade of an older site which has a different ranking system and website: http://mathschallenge.net/index.php?section=project.

Your profile consists of the number of problems you have solved. Your ranking is based on levels. If you have successfully solved 25 questions you qualify to the level 1 and so on and so forth. On solving a problem its thread gets unlocked and you can check solutions of others in the languages they preferred. Thus, you can compare your code with others.

Your profile gets dissolved if no activity happens in 90 days of time. This happens if you are 1 or 2 level programmer. Level 3 and level 4 programmers are granted immortality, thus, here lies the advantage of being superior.

Mathalon
http://www.fameoflight.com/Mathalon/

Mathalon is open alternative to Project Euler. Where user are allowed to add more problems. The system is fast developing and ideas are implemented quickly. If you have any idea or suggestion go for it, It will not go unheard.