JSON-RPC is lightweight remote procedure call protocol. It is designed to be simple!
It all depends on your language(s), your library(s), your environment(s), and your transport(s).
The original
json-rpc site has a list of
implementations.
Wikipedia has a list of
implementations.
Some members/managers of the group maintain implementation(s).
There are a lot of sites and posts about json-rpc.
If you have questions about a specific implementation, ask the author first!
Otherwise ask at the
json-rpc google group.