GemCraft:

Havoc and corruption swarms through the land, and you are one of those few wizards who can put an end to it. Create and combine magic gems, put them into your towers and banish the monsters back to hell! Controls: click on spell buttons to select them< drag gems to move, throw or combine them< 1-6 or B/T/C/M/W/G selects spells hold ctrl to create/combine as much gems as possible hold shift to place multiple towers/trenches hold shift to create multiple gems P to pause click/space/enter to close tutor panels