The ZeroMQ Process: C4 (gitbooks.io)
When we say ZeroMQ we sometimes mean libzmq, the core library. In early 2012, we synthesized the libzmq process into a formal and reusable protocol for collaboration that we called the Collective Code Construction Contract, or C4. You can see this as a layer above the license (e.g. MPLv2). These are our rules, and I'll explain the reasoning behind each one.