Command-line tool for sending and receiving ZeroMQ messages on any socket type (REQ/REP, PUB/SUB, PUSH/PULL, DEALER/ROUTER, and all draft types). Supports Ruby eval (-e/-E), script handlers (-r), pipe virtual socket with Ractor parallelism, multiple formats (ASCII, JSON Lines, msgpack, Marshal), Zstd compression, and CURVE encryption. Like nngcat from libnng, but with Ruby superpowers.