QuakeBuilder 0.1 totally kind of works with unmodified WinQuake and GLQuake clients. It has an entity limiter! It doesn't need specular highlights or cubemaps! It doesn't have any new maps with r_speeds in the 5,000s! It doesn't even try to wow you with new monsters!
But don't let that turn you off!
You can turn off the entity limiter! You can play id1-compliant maps with r_speeds in the thousands! QuakeBuilder also runs in fitzquake and aquirRe's GLQuake engines! Hell, it might even work in some build or another of DarkPlaces! I don't know! I've never tried it!