MSRP Clients
This is a list of clients supporting or planning to support the MSRP relay extension:
Blink client for OSX, Window and Linux from http://icanblink.com (supports relay extension)
SIP SIMPLE client Python library from http://sipsimpleclient.org (supports relay extension)
Java SDK http://msrp.java.net/
C++ OPAL SDK from http://www.opalvoip.org (roadmap)
SIP Communicator from http://sip-communicator.org (roadmap)
Mercuro - fully featured IMS client from http://www.mercuro.net (MSRP but no relay support yet)
Radvision MSRP Client Developer Solution from http://radvision.com (supports relay extension)
There may be others but things in this realm are changing fast so do not rely on this list to be up to date.