Jack-o-Nine-Tails is more centralized image wise, Whoremaster is similar with community made slaves, Brothel King has girl packs that are ranked by image count. The best images are probably in Jack-o-Nine-Tails, but the game itself is honestly not for everyone. Whoremaster is similar to Slave Maker with much more emphasis on running a brothel. Brothel King has the whole sex training thing, but no day mode. Jack is probably the closest you'll get to Slave Maker. Of course, you could also try the Princess Maker games that Slave Maker is based off of. There's no sex, but they're good games.