That sounds like Mugen to me. Strictly speaking, it's not so much a rape game as a fighting game engine for which rapable characters and rapists have been made or been edited from existing characters. There are a few threads for it on this forum already, as well as elsewhere. Here's one: http://www.ulmf.org/bbs/showthread.php?t=629
15 pages, so it'd take a while to read through completely, but the links for the game pack (engine, characters, stages and music) provided there still seem to work, and (if memory serves) the thread contains a significant amount of information about how Mugen works and how to make it do what you want, as well as additional content and links to related sites.