for hentai fans that can understand Japanese or can figure out how to play the game just by memory of what dose what. the games at this site are what the Japanese call net games or as us Americans in general call browser mmo. most of these are card based some are very story driven and some are just weird. you can log in using Facebook or Google so anyone can play them even those from the US.
http://www.dmm.co.jp/en/netgame/