There is only two games I know to not have DRM, one is being Windward but that game is also on GOG.com so doesn't deserve a mention.
The other one is SoulSaber 2: Soul Saber 2 on Steam
It is an arena game with similar base machincs like Virtual-On but with larger roster and more characters fighting each other at the same time. Rock-paper-scissor, a type of character always counter an another and have disadvantage against a third. Originally it is a game from 2008 or so, just for some reason this unknown game got released on Steam not a long ago. :)