The latest open-source project worthy of its own shout-out on Phoronix is BGFX, which via its library allows seamless targeting the Direct3D 9 and Direct3D 11 APIs on Windows platforms. For all platforms, targeting BGFX means OpenGL 2.1, OpenGL 3.1, OpenGL ES 2.0, and OpenGL ES 3.0 rendering support.
BGFX is used by a few games right now for easily targeting multiple rendering APIs across multiple platforms. The officially supported platforms right now include Google Android, Apple iOS, Linux, Google Native Client, OS X, and Microsoft Windows.
BGFX also has its own cross-platform shader language (shaderc) that is derived from OpenGL's GLSL syntax. BGFX is put out under a 2-clause BSD license. BGFX is under active development and supports many features, with more details being available from the BGFX GitHub page.
A similar project worth mentioning again is Waffle, which allows for run-time selection of the OpenGL (or GLES) version target and dynamic windowing system support.