The first generation, Unreal Engine integrated rendering, collision detection, AI, visibility, networking and file system management into one complete engine.
One of the bests game engines out there, I love this engine despite having some limitations that requires a lot of workaround, it have powered a few of my all time favorite games such as
Deus Ex (My all time favorite game)
Unreal - RTNP
Tactical Ops (yeah that mod who became a retail game)
(I would liked to mention a few other games like Nerf Arena Blast or Mobile forces, but while these games have some appeal and some more or less unique features they are a bit flawed on their own end ...)
Though Great engine with great capabilities. I saw many things implemented through mods and games to see how powerful it is.
I mean it can perform pretty much anything that a modern FPS can do. It might only be limited by the physics still but in therms of interactivity it does pretty much everything and all without much power consumption from the CPU.
The real shame about it is the fact that the engine hasn't entered to the public domain, I would love to see it being upgraded and have even things like being used to power games through a browser which would have been awesome.