The military MMO Armored Warfare is currently playable for everyone. They want to test the servers.
Armored Warfare is designed as a competitor to World of Tanks, but with modern tanks, not focused on World War II like WoT. There have already been several limited-time closed beta phases called Early Access.
Now they are open to everyone, starting a stress test in preparation for the open beta. The test lasts until Sunday at 20:00 our time. You can download the client on this page for Armored Warfare after you have registered.
However, they warn: There may be lag and queues during this stress test.