Seeing all the gameplay being posted of Dr. Robotnik's Ring Racers has made me rather curious about the state of vidya engines. Looking at just how much the Doom Engine has been modified to the point that there's even a kart racer built using it made me wonder about all the other engines that have come and gone over the years and just how verisitile those could still be if people put in the effort to use them. Are there any other engines actively being supported or have they nearly all fallen by the wayside? Also, what are some "promising" new engines that are being independently developed?