ZigBee stack for free:

Texas Instruments has announced a ZigBee stack, Z-Stack, for download.Z-stack is compliant with the ZigBee 2006 specification and supports multiple platforms including the CC2430 system-on-chip solution for IEEE 802.154/ZigBee and a new platform based on the CC2420 transceiver and TI’s MsP430 ultra-low-power microcontrollers (MCUs).
Z-stack supports features like over-the-air download, which allows updates of nodes wirelessly over a ZigBee mesh network, and CC2431, which features location awareness. This enables the users to create new ZigBee applications that can change behaviour based
on the nodes’s current location.