So opengl does support freebsd,
Mesa works with software rendering too. It'll be slow but it'll work.
Again, you don't need to do anything "special", graphics/libGL is part of the complete x11/xorg install.
Okay last question :Handbook: Chapter 4. Installing Applications: Packages and Ports
No,I think it is mesa-libs.See for yourself http://www.freshports.org/graphics/mesa-libs/graphics/libGL was recently deleted. I think it has become graphics/libGLU (utility), and maybe partly graphics/libGLW (widgets).
Dr.Topaz , learn how to use the Handbook, command-line utilities for ports, and FreshPorts.