Bit old, but pretty much everything Source Engine is self-hostable isn’t it? Most of them even come with a pre-configured SRCDS (SouRCe Dedicated Server) you can download and run right from the steam launcher.

I know I ran a GarrysMod server for quite a while; piling a shit ton of mods on it. Plus any source game you’ve got installed, Garrys Mod can and will use the resources/assets from.