Click
here and download the free edition of GameMaker Studio. Once installed, run it and the first screen should say "Standard edition, free for a limited time". Click it, put in your email address, and you will get a registration code for the Standard edition for free. This removes all the demo version limitations. Normally costs $50.
On top of that, if you want the Pro version you can upgrade to it for $35 (normally $99).
GameMaker is pretty capable. Games like Hotline Miami, Gunpoint, the original Spelunky, etc were all made with it. It's pretty easy to use, has some built in tutorials to get you started. Grab a key, make a game. Its kinda fun.
