Bukkit

Features:

• Support multiworlds.
• The border does not push you, but causes some damage when you get out the border.
• Ability to select multiple areas in the same world, for stay of players. (This way, you can create a zone of complex shape)
• There are "floor" and "ceiling" in the zone. (You can deny fly in the clouds and dig deep.)
• Store areas in the database. (SQL used)