Mesa was originally designed for Unix/X11 systems and is still best supported on those systems. All you need is an ANSI C compiler and the X development environment to use Mesa.
The DRI hardware drivers for the X.org server and XFree86 provide hardware accelerated rendering for chips from ATI, Intel, and NVIDIA on Linux and FreeBSD.
Drivers for other assorted platforms include: the Apple Macintosh and Windows.
Details about particular drivers follows: