Tabula Rasa. It was a first/third person sci fi mmo shooter/rpg with craftable mechs, It lasted for a bit more then a year before it shut down, and no private servers have ever been created.

Gundam : Universal Century Online. Picture Star Wars Galaxies with combined arms mecha warfare. Start on foot, buy a jetpack, mine some ore, built a tank/jet/mech, fight in the war. It lasted about as long as tabula rasa before it shut down. It currently has no private server.

Firefall. First/third person sci fi mmo shooter/rpg with craftable mech suits. bla blah, shut down no private server ever created.

tl/dr: I want a new mech mmo. Or even just to be able to play my old favorite mecha mmos.