The name Cap'n Proto actually originally meant "Capabilities and Protobufs" -- it was a capability-based RPC protocol based on Protocol Buffers. However, early on I decided I wanted to try a whole different serialization format instead. "Proto" still makes sense, since it is a protocol, so I kept the name.

The pun "cerealization protocol" is actually something someone else had to point out to me, but I promptly added it to the logo. :)

https://en.wikipedia.org/wiki/Capability-based_security

https://capnproto.org/rpc.html#distributed-objects

The idea really goes way beyond security and RPC. It's hard to explain concisely but it's sort of a way of thinking about software architecture.