We present Muddleware, a communication platform designed for mixed reality multi-user games for mobile, lightweight clients. An approach inspired by Tuplespaces, which provides decoupling of sender and receiver is used to address the requirements of a potentially large number of mobile clients. A hierarchical database built on XML technology allows convenient prototyping and simple, yet powerful queries. Server side-extensions address persistence and autonomous behaviors through hierarchical state machines. The architecture has been tested with a number of multi-user games and is also used by non-entertainment applications.