Execute the command when the player has reached cords by Y, entered/leaved a region, died/respawned, or joined/quited the server (Y cords can be either from top to bottom or from bottom to top)

Block any explosions in any worlds on your server

Make flying harder on your minecraft server

Limit items that player can put in his enderchest (You can also create groups)

A Minecraft plugin for automatically removing old log files.