ZigBee is a protocol that works on the 802.15.4 spectrum (WiFi is also known as 802.11 for its slice of spectrum.) As a short-range, low-power protocol, ZigBee is suited for two-way communications among small devices, and can be used to build self-organizing networks of devices.
The open source community is transitioning to create advanced Web-centric consumer devices using high profile open source based distributions and a wide range of high-performance, low-power ARM(R)-based SoCs.