Mycel is a single-file, pure-Ruby RPC library built around perfect role symmetry: once a TCP connection is established, either side can invoke any method exposed by the other — there is no client and no server, only peers. Each connection is one hypha; each Endpoint is a node in your own programmable mycelial mat. Layered architecture (Framing / Transport / Channel / RPC), pluggable codec, backpressure, pluggable executor, and zero monkey-patching of Ruby standard classes.