They have fraps, but some of them use dxtory and have fraps as a backup.
There are some different ways you can film in gmod, probably the worst way obviously is with your own camera. Or for a free program but not the best quality, use wegame.com which lets you film in-game. Or you can get fraps for 30 dollars or if you're so illegal, download it using a torrent. I'm not encouraging you to do this but just letting you know, it is there. -Hyper Sniper
I think you can use portal in gmod 10, but I'm not so sure.
runOnTick(1)
use fraps fraps.com
They use software called FRAPS
mostly fraps
If you want to make models for gmod look at XSI Mod Tool.
Can i download fraps on Xbox 360
I use FRAPS.
download them from garrysmod.org
I think bandicam / fraps premium + HD