3D hardware acceleration
3D hardware acceleration requirement can be tricky in the free software world as most hardware manufacturers don't provide enough information for the writers of free drivers nor release their own free drivers. There is plenty of confusion around this issue because many people don't care whether the required firmware is freely licensed and make statements that muddy the waters.
Intel[edit]
Intel is your best bet for properly working hardware accelerated 3D. Intel has freely licensed firmware and driver that they support. Unfortunately Intel GPUs hardware sold after 2008, depends on the *Management Engine and is incompatible with POWER9 hardware. Old Intel GPUs are limited to OpenGL 2.0.
AMD[edit]
AMD (formerly ATI) has a free driver they support but their firmware remains proprietary. You will not get hardware accelerated 3D on AMD with free software. AMD has released specifications for many of their cards. There are is a libre reimplementation of AMD Southern Islands GPU ISA called MIAUW, but this incomplete and cannot be used to synthesize a working GPU design. By contrast AMD has made a high performance processor called the Opteron (designed by Mitch Alsup) which might be good enough to do software rendering. Currently there is no reverse engineering effort of those AMD GPUs.
Nvidia[edit]
Nvidia supported an obfuscated 2D only driver for some time in the past. They have not released any specs.
nouveau[edit]
There is a reverse engineered free software driver+firmware, nouveau, which is not supported by Nvidia at all. nouveau enables hardware accelerated 3D for some Nvidia cards.
OpenPOWER[edit]
The IBM POWER9 has enough horsepower to play 3D games using multithreaded software rendering.
PowerVR[edit]
There is still no free software driver. This is also used in some older Intel chipsets, as well as on the BeagleBone and OpenPandora.