id Software often gets credit for opening the source code of old game engines a few years after their release. Epic Games has now pulled a comparable feat, except with two major differences: the new Unreal Development Kit doesn't include game-engine source code, but it does give developers all of the tools they need to create standalone titles using Unreal Engine 3, Epic's latest and greatest engine, free of charge.
Unreal Engine 3 powers a wealth of current and upcoming titles, including the Gears of War series, Unreal Tournament 3, the BioShock series, Borderlands, the Mass Effect series, Mirror's Edge, Tom Clancy's Rainbow Six: Vegas 2, and many more.
According to Epic, the Unreal Development Kit features the "most recently added features and technological enhancements, including many that have yet to be seen in an Unreal Engine game." The company also intends to deliver "ongoing, upgraded builds of UDK for free." UDK tools include Epic's Unreal Editor level-editing software, plus the following:
Unreal Content Browser, a revolutionary tool for browsing, searching and organizing game assets with collaborative metadata tagging system. UnrealScript object-oriented programming language and Unreal Kismet, a visual scripting system that enables rapid prototyping on the fly. Unreal Matinee, a powerful tool with movie director-class controls for building in-game cinematics and gorgeous cut scenes. Unreal Cascade, an advanced particle physics and environmental effects editor that aids the creation of fire, fog, explosions and other visuals. NVIDIA® PhysX®-powered physics system with Unreal PhAT visual modeling tool for creating character and object physics rigs. Unreal Lightmass, a global illumination system that dramatically lights and shadows with minimal effort required by artists and designers. AnimSet Viewer and AnimTree Editor, which give animators precise control over every muscle and bone movement.
You can grab the UDK and associated documentation here on the official website. Usage is free for non-commercial endeavors, but Epic also says it offers licensing options with terms favorable to independent developers.
Epic stresses that games built using the UDK are completely standalone, so they'll run happily on any PC without a copy of Unreal Tournament 3 to latch onto. (Console support is currently "under consideration," however.) The UDK Showcase already includes a couple of sample games from third-party studios, including one title that was originally a UT3 mod.