BNU Online Judge

Older releases on Google Code: http://code.google.com/p/bnuoj

An Online Judge system for Beijing Normal University, featuring following awesome functions

Basic online judge functions;
Virtual judge functions, including loads of OJs;
Replay contests and merge standings;
Contest with challenge sections, like Topcoder and Codeforces;
Problem categories, delicious for new comers.

And it's still developing!!

Version 3:

http://www.bnuoj.com/v3

http://acm.bnu.edu.cn/v3

http://oj.51isoft.com/v3

Version 2:

http://www.bnuoj.com/bnuoj

http://acm.bnu.edu.cn/bnuoj

http://oj.51isoft.com/bnuoj

Version 1:

http://www.bnuoj.com/contest

http://acm.bnu.edu.cn/contest

http://oj.51isoft.com/contest

OI version:

http://www.bnuoj.com/contestoi

http://acm.bnu.edu.cn/contestoi

http://oj.51isoft.com/contestoi