Kenton Varda (the author of Cap'n Proto), was the primary author of Protocol Buffers version 2. Quoting from https://capnproto.org/index.html https://capnproto

Kenton Varda (the author of Cap'n Proto), was the primary author of Protocol Buffers version 2. Quoting from https://capnproto.org/index.html https://capnproto.org/index.html Because it’s easy to pick on myself. :) I, Kenton Varda, was the primary author of Protocol Buffers version 2, which is the version that Google released open source. Cap’n Proto is the result of years of experience working on Protobufs, listening to user feedback, and thinking about how things could be done better.