Gemcraft is a classic tower defense game with a twist. You use mana earned from killing monsters with your gems to create more gems, turn gems into bombs, put up more towers, build trenches, and combine gems. there are several types of gems. triangle gems are the weakest, then squares, diamonds, and so on. Also, each color of gem has a property. When you mix two gems of different colors together, you get a cross-color gem. This gem has weakened properties of both of the other gems.
The goal of the game is to defeat all the monsters in all the levels and make your journey to the far east.