My current game project is creating a high-speed gaming network, specifically optimized for League of Legends but also extendable to other games down the road.

I have a very early version ready for testing, but it only supports UDP tunneling, not TCP. I certainly need to add TCP tunneling as well but that is still a few weeks away even if it goes smoothly. In the meantime, I'd like to find a free-to-play Windows 7 game that does not use TCP, only UDP, to test my tunnel/proxy with. Anyone know any?

I've tried several games (League of Legends, TF 2, Dota 2, Netrek) but none of them work since they all use a combination of TCP and UDP and expect the client IP address from TCP to match the client IP address from UDP.

Maybe the original StarCraft? Don't know if it's free.
The open source releases of Quake are free to play, and use TCP. Try Quake III.

Quake 3 is pure UDP. Not sure about Unreal tech. Wouldn't be surprised if they were also pure UDP.