My company is currently in the process of developing a suite of
applications using ULC (Ultra-Light Client by Canoo http://www.canoo.com/ulc/) as the rich client platform. ULC uses
HTTP(s) as a protocol with servlets, RMI/IIOP with EJB containers.
According to the technical contacts I have at my company, other
protocols are possible as extensions, but have not currently been
added to the framework by the folks at Canoo.