IEEE 802.15.4 networkong stack covers PHY and MAC layers (PHY layer implemented in hardware and MAC optionally implemented in software). Also 6lowpan (IPv6 packet encapsulation) is implemented for use by IEEE 802.15.4 and BT LE networks.
Note: due to licensing restrictions (and despite project's name) we do not plan to implement any ZigBee related stack parts.
OpenMAC is a TinyOS-based implementation of IEEE 802.15.4 MAC layer, which lies at the core of MeshNetics ZigBeestack, and provides basic wireless networking (star,peer to peer) to WSN's. Available for low-power ZigBit modules and Atmel AVR Z-Link Kits