Prime World: Defenders was released for the PC/Mac sometime in 2013 – last month, this card collecting tower defense (TD) game, now simply called Defenders was released for the iPad (you can also check out appSIZED’s review of Man At Arms TD, which employs the same mechanic).
There is a story to this game and your mission mainly is to defend powerful and valuable prime (crystals) from the Touched (enemies or creeps, in TD parlance) who want to take it for themselves. Caught in the middle of two warring groups trying to control the resource, your job is to keep them away using various powerful towers.