I believe Chyoo is no longer being maintained, but is kept up on the internet. I don't know if you can still sign up. There are a few choose your own adventure games on Literotica (
www.literotica.com). The Breast Expansion Archive (
http://www.bearchive.com) has an Addventure choose your own adventure game. The last time I looked at it (several years ago) it was very extensive and you could read and add to it for free, but it looks like it may no longer be free, or maybe it isn't there now. I believe Addventure is a free program for creating choose your own adventure games on the internet. There are probably other erotic choose your own adventure games that can be found through searching.