Play Left 4 Dead 2, if you want I guess.

Tully's Vanilla Experience
173.208.184.235

Only have 4 custom maps right now;
Yama, Urban Flight, 2019, Suicide Blitz
Edit: There are 16 custom campaigns added to the server.

Supports coop, survival, & mutations.

Find it in the community group server browser, or open console and paste:
connect 173.208.184.235