DungeonsXL is a server mod that allows you to instantiate worlds.
Its main goal is to offer a way to use a world in a set state multiple times by a player (like for a jump'n'run), a group of players (e.g. for a quest dungeon, an adventure map or a PvE arena) or even by groups of groups of players (e.g. for PvP arenas). DungeonsXL also provides custom game mechanics to make these worlds interesting. It might also be helpful if you want players to build something in creative mode quickly and uncomplicated without any influence on their main world data (inventory, levels etc.).