Buxville is a fast, long-running Minecraft server. They have a stable base of reliable administrators and moderators and an active, continuously-expanding community. Buxville uses a Roles system that transforms the sandbox game into an RPG that features a real economy and encourages players to interact with each other.
Buxville has its own XML-RPC API, which pulls data directly from the Buxville database. Any player with a good idea for an application or interface can request a private API key.