They are compiled as separate libraries, so you can use the serialization layer without linking in the RPC layer. But if anything it was the serialization that

They are compiled as separate libraries, so you can use the serialization layer without linking in the RPC layer. But if anything it was the serialization that distracted me from the RPC. Cap'n Proto was originally (briefly) a capability-based RPC system on top of Protobufs. :)