This is protobuf-c, a C implementation of the Google Protocol Buffers data serialization format. It includes libprotobuf-c, a pure C library that implements protobuf encoding and decoding, and protoc-c, a code generator that converts Protocol Buffer .proto files to C descriptor code, based on the original protoc. protobuf-c formerly included an RPC implementation; that code has been split out into the protobuf-c-rpc project.