CodeAbbey - website with programming problems for those who want to improve coding skills. Algorithms, basics of Web, Assembly, Brainfuck, even HTTP-based games. Anyone is welcome!
In September 2013 I tried to improve my knowledge of web-development basics. As a project I decided to make interactive collection of programming problems. Like ProjectEuler, but with no relation to math.
It went a bit too far: now there are over 30000 users :o This community sometimes make me learn new things myself :)