Think you can do a better job of arranging high-polygon concrete barriers than the folks at Crytek? Good news. The developer has released the CryEngine 3 SDK, which puts you at the helm of the same engine that powers Crysis 2.
The 659MB download is available free of charge at Crydev.net. Some restrictions apply, however. While the SDK is free for non-commercial use, you'll have to get a development license if you intend to make any money with games based on the engine. Crytek says it has "attractive options" for independent studios who would like to use the engine. It's also encouraging educational institutions and students to take advantage of the SDK.
Crytek isn't the only one making a full SDK available to the public, of course. Epic's Unreal Development Kit has quite a following, and it's set to spawn a number of interesting games, including Q.U.B.E. and Hawken. It'll be interesting to see how games created using the CryEngine 3 SDK stack up.