Twirp - Simple RPC framework with protobuf service definitions.
tarpc - RPC framework for Rust with a focus on ease of use.
Simple GoRpc - RPC explained by writing simple RPC framework in 300 lines of pure Golang.
Facebook Thrift - Serialization and RPC framework for service communication.
NNG: Lightweight Messaging Library - Lightweight, broker-less library, offering a simple API to solve common recurring messaging problems, such as publish/subscribe, RPC-style request/reply, or service discovery.