Robocraft

[Tmon]

Found out about this from a friend a few days ago.  You build vehicles out of blocks that you then use to fight in an arena.  You earn research points and credits in the arena which are then used to research and buy new types of blocks.  You start out with a fair number of basic blocks and three prebuilt vehicles in the garage.  The tech tree is basically unlocking more powerful versions of most of the blocks and the few types that don't come as part of your starter blocks are easily unlocked.  This means you can build any type of vehicle from the start, although the higher tier blocks make them better fighters in the arena.  The game is free to download and offers the standard micro trans stuff.  You can play for free or buy premium time which gives a bonus to RP and Credits and you can also use premium currency to buy researched blocks.  The grind for higher tiers is fairly long on a standard account but since I like building more than fighting I'm not motivated to buy premium time or currency.

http://robocraftgame.com/