Nouveau: Accelerated Open Source driver for nVidia cards
The nouveau project aims to build high-quality, free/libre software drivers for nVidia cards. “Nouveau” [nuvo] is the French word for “new”. Nouveau is composed of a Linux kernel KMS driver (nouveau), Gallium3D drivers in Mesa, and the Xorg DDX (xf86-video-nouveau).
2D/3D acceleration supported on all cards; see FeatureMatrix for details
Performance level selection (also known as "reclocking") is not supported yet. Expect low 3D performance on laptops using a Tesla GPU and all Fermi/Kepler cards. (see CodeNames)
Dec, 2013: H.264/MPEG4 decoding for cards with VP3/VP4.0 engines merged into Mesa
Sep, 2013: NVIDIA is willing to help Nouveau with documentation and answering some questions! Yay!