I played RTCW and ET for years, both for fun and competitively. They are amazing games that are absolutely simple to mod with unending mods out there. For both games there are bots such as Fritzbot that really feel like playing with other players. They can be dumb, but you can fill a server and they will play the objective, even doing some of the stuff common of the time like getting in your face and shaking around, tking during warm up, and tea bagging. The bots even work for the hundreds of custom maps out there for both games MP. This is the pinnacle of the Quake engine and tons of fun. There are still MP servers running, or just grab the bots and have fun!