Mark Overmars' Game Maker engine is a key learning tool for budding gave developers. By abstracting game creation with simple drag-and-drop functionality, Game Maker allows beginning users to easily build working games without programming. Those wanting to go deeper can utilize the Game Maker Language to script complex game logic, as well.
This, combined with the tool's nominal cost, has lowered the barrier to game development to almost nil. But don't assume that amateur hour is the rule of the day. Standout indie titles like Spelunky and Seiklus are creative examples of what is possible with the tool. (Gamasutra, November 17, 2010.)
Read more about Mark Overmars and Game Maker on Answers.com and on YoYo Games Glog.