Part of the internals of Rigelian are available as open source software.
ConnectorProtocol is a generic protocol specification to control a network based music player for Swift. The protocol abstracts a player specific implementation from a client implementation, which allows to have a single client that supports multiple player types.
MPDConnector is a full implementation of the ConnectorProtocol interface specification, based on libmpdclient. It can be used to control a mpd-based music player.