SOJ is an open source project, which is developed by Wilbur Ding and Liang Sun.
SOJ means Small Online Judge, which is an online judge system, that is a system to test the correctness of programs.
SOJ can compile and execute your code, and test your code with pre-constructed data. Submitted code may be run with restrictions, including time limit, memory limit, security restriction and so on. The output of the code will be captured by the system, and compared with the standard output. The system will then return the result. When mistakes were found in a standard output, rejudgement using the same method must be made.
SOJ also has a rank list showing users with the biggest number of accepted solutions.
The source code of this project can be found on Google Code.
The project is currently deployed here, and you may have a try.