ZONE games aren't really games, but sweet Jesus does 4chan love them and each one is well-made. Another Illusion game, so it's good stuff as usual.You can create a classroom with 25 students complete customizable (the male customizations are really poor compared to the female ones) and then see how they react with each other.
You play it like an old first-person dungeon explorer, only with random naked chicks to play with.
The sequel is more of the same, with a more convenient map and animations in some scenes. There's a limit to how long you can maintain the pocket world that serves as your hunting grounds, and losing fights or letting your girls escape depletes it.
The demo goes until the first boss and gives a good idea of the game.
You can get it and the full game from the author's blog: You play as Raidy, an adventurer, wandering the continent of Else.
Different artists worked on the visual art, so they're not all so awesome; not like a leech-girl could look better anyway.
There is also a worthy sequel, and the finale released.
No eroge novels (aka 'erotic visual novels') in this list: there are so many of them that we have made a page just for them.
We also have a page for Adult interactive Fiction for smut made by non-Japanese writers.
You are a new principle at a failing school, and make it your personal mission to corrupt the students, PTA, and entire city.
You can employ anything from charisma to blackmail to optional hypnotism.