What are the differences between the branches? (ie. opfor, opforfixed, etc)

[sofakng]

Which branches are considered the current or latest for Half-Life, Opposing Force, and Blue Shift?

It looks like Half-Life (master branch) and Blue Shift (bshift) are self explanatory but what about Opposing Force? (it has opfor and opforfixed)

Also, are there any other branches with interesting fixes or changes?

[FreeSlave]

opforfixed is basically the hlfixed changes applied to opfor.

[nekonomicon]

Also, hlfixed and opforfixed branches was made specially for this assemblies

[nekonomicon]

Also, are there any other branches with interesting fixes or changes?

gravgun branch has hl2dm parody, sandbox and coop for half-life, but full assets was not released yet.
You can find different parts here:
http://mittorn.fwgs.ru/coop-entpatches/
http://mittorn.fwgs.ru/ggm/
https://github.com/nillerusr/gravgun-extras

aghl branch can be compiled without client as miniag mod and server library in this case can be used in normal half-life.
sohl1.2 branch can be compiled with -DXENWARRIOR=1 flag to use libraries for Xen-Warrior

[nekonomicon]

dmc branch currently contains "DeathMatch Classic: Adrenaline Gamer Edition" + "ThreeWave CTF" code.