This paper presents a new multiagent middleware named Siebog, made to provide high performance and platform independence for software agents. This framework was built by combining the features of the Radigost and XJAF agent frameworks. It provides an infrastructural support for both client-side and server-side agents. The clientside agents are written in JavaScript and can be executed on a wide variety of software and hardware platforms, including desktops, smartphones and tablets, and Smart TVs. The server-side agents, on the other hand, can harness the benefits of clustered environments, and rely on automated load-balancing and fault-tolerance for the uninterrupted delivery of services. The two sides of Siebog have been integrated in a way that enables cross-platform messaging, agent code sharing, and even heterogeneous agent mobility.