Looks like game developers took notice of the potential lying within the indie scene, and they're increasingly making things easier for them to get into the market. If a few days ago Unity Technologies released a free version of its engine targeted towards hobbyists and aspiring developers, today is the turn for the very same Epic Games, who released what essentially is a non-commercial version of its Unreal Engine 3, perhaps the most widely used engine in commercial games during the last years, including some really big hits like Gears of War, BioShock or Mass Effect.
Unlike Unity, this looks to be a full-fledged version, except for its non-commercial use (those wishing to publish the game later, can take a look at the licensing terms), and the limited compatibility scope. While the engine can usually target games developed either for the PC, the XBOX 360 or the PlayStation 3, the UDK is restricted (for now) to the PC. There's more information about other things at the official website listed above, and a good summary over at ShackNews, along with the tools available for download.