I believe this is the first fully free Zigbee stack implementation for MCUs. The mainstream stacks are vendor-locked: restricted to specific platforms (usually the corresponding vendor’s MCUs) and released under custom licenses.
It implements only the RFD subset (no routers), but that is enough for most battery-powered hobby DIY devices used in home automation.
The project is also a demonstration of my Pulse framework, with its C++20 coroutines applied to a complex real-world project. The whole stack is built on the cooperative tasks, timers and synchronization primitives provided by Pulse, which lets the asynchronous protocol logic — timeouts, retransmissions, polling, multi-step exchanges — be written as straightforward sequential code instead of explicit state machines.