Virtual Judge is not a real online judge. It can grab problems from other regular online judges and simulate submissions to other online judges. It aims to enable holding contests when you don't have the test data.
Virtual Judge currently supports the following online judges:
POJ
ZOJ
UVALive
SGU
URAL
HUST
SPOJ
HDU
HYSBZ
UVA
CodeForces
Z-Trening
Aizu
LightOJ
UESTC
NBUT
FZU
CSU
SCU
ACdream
CodeChef
CF::Gym
OpenJudge
Kattis
HihoCoder
HIT
HRBUST
EIJudge
AtCoder
HackerRank
51Nod
TopCoder
E-Olymp