Most games had custom engines in the early 2000s. There was very little sharing of tech. Chaos Theory used Unreal, Prince of Persia used Jade, and Far Cry used the CryEngine. The only commonality, at least from an anim perspective, was the authoring package. Everyone used 3dsmax and CharacterStudio.

I was one of those folks. Stealth kills, wall jumps, and ledge grapples were the highlights. This was the first time I worked with an Animation Director. I may have been proficient with software, but Gilles Monteil became a huge influence on performance.