Browser games, each with its own revision log. Open a game's log to see what changed from build to build and play any copy that survived. Newest game first.
Pick a teacher (Mr. Stephgarner, Mr. Ras, or Mrs. Ward) and fight through three haunted wings of a castle school, building a deck of cards as you go.
Pick a staff member and survive waves of monsters through the hallways, cafeteria, gym, library, and boiler room with automatic attacks and upgrade cards.