Big (epic?) news today. Epic Games has just launched a free edition of its Unreal Engine 3, one of the best (if not the best) game engine around to use when developing 3D games. Called the Unreal Development Kit (UDK), the toolset is also distributed with support resources and technical documentation which are all available to download from the official site.

No charge will be imposed for noncommercial and educational use of UDK, although you will still need to obtain an official licensing agreement (Epic receives twenty-five percent of revenue after the first $5,000 is made) to develop a commercial product using UE3.

The UDK site is already hosting two standalone games that runs on the new UDK framework, meaning that you won't need to have Unreal Tournament 3 installed to play them. The Ball deserves a bit of a special mention though, because it was originally developed as a mod for UT3 (hence the need for the full game to play it), but has since then been turned into a standalone version using UDK to showcase the versatility of the engine.

Epic Offers Free UE3 For Non-Commercial Use (Gamasutra)
UDK Version 1.0 - beta release mirrors (Epic Games Forums)