CapnRPC is an "amusingly-christened" XML-RPC client written for PLT's MzScheme/MrEd Scheme environments. In its current state it's a little rough-around-the-edges but fully functional. It is tightly integrated with Scheme functions and their wonderful first-classness.
Matt Jadud has written XchemeRPC, an XML-RPC library for the v200 version of PLT's Scheme software. It uses nearly the same curried client interface as CapnRPC, but it supports marshalling of more datatypes (vectors, for one) and has the added feature of being an XML-RPC server as well, a capability completely absent in CapnRPC. If you're running the latest PLT Scheme be sure to check out XchemeRPC.
> (define srv (xml-rpc-server "betty.userland.com" 80 "/RPC2"))
> (define getStateName (srv "examples.getStateName"))
> (getStateName 41)
"South Dakota"
There is now a CapnRPC mailing list through Yahoo Groups. Subscribe to get updates on when new versions of CapnRPC are released.