SDL 2.0 has been in development for years with many features. The library is used by many games and applications for simple yet cross-platform interaction with graphics/sound/input devices. Recently its taken a big step up due to one of the project leaders being hired by Valve to work on the Steam Linux client.
Among the features of SDL 2.0 are full 3D hardware acceleration support, OpenGL 3.0+ support, OpenGL ES support, multiple window/display support, multiple audio device support, a simple 2D rendering API, force feedback support, X Inpout 2 support, power management support, 32-bit audio, better fullscreen support, and a whole lot more.
Valve is already planning to push SDL 2.0 into their Steam Linux Runtime in the next day or two, which will be important for the Steam Box. Another important change is that SDL 2.0 has been relicensed from the GPL to Zlib, so that it can be statically linked by commercial closed-source games.
The release announcement for the long-awaited SDL 2.0 release can be found on the mailing list and more information can be found on the SDL Wiki.