The best replacement for zigbee is bluetooth.

The best alternatives to zigbee are rated as following:
★★★★★  bluetooth
★★★★  wifi
★★★  z-wave
★★★  xbee
★★  insteon
★★  z wave
★★  x10
★  zigbee pro
★  rfid
★  bluetooth low energy
★  802.15.4
★  ble
★  6lowpan
★  digimesh
  rf
  ant
  zwave
  uwb
  rf4ce

Your alternative for zigbee is not listed? Suggest!
Speaking about zigbee, one probably shouldn't forget about microcontroller.

Other search terms related to zigbee and their ratings are:
★★★★★ microcontroller
★★★ msp430
★★★ pic microcontroller
You have in mind a companion for zigbee and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of zigbee in all years. Click on graph for more.
zigbee
bluetooth
wifi