They are using a Custom Java Server.
Initially this was L2J, but they formed a small team and started modding it, removed anything that shows its L2J....
you can see some areas still have some interesting issues that l2j had, like stucking maps and so on, but this is being worked too.
Right now this is 'not' L2J anymore since they did enough Mods and Rewrittings here and there.
But what we can say is that this works.
Maybe not as L2OFF, but w/ many features and content (Specially after Innova Russian HTMLs Leaked ofc)