KarlP from the website “False and misleading information” has written this AVR code library for the MRF24J40 802.15.4 radio chip.
The MRF24J40 operates in the 2.4 GHz band and supports ZigBee™, MiWi™ protocols and proprietary protocols. It interfaces with an MCU via a four-wire SPI interface.
Hi! Just saw my own name come up in my DP rss feed :)
There’s also an arduino library: http://false.ekta.is/2011/03/mrf24j40-with-arduino-teensyduino/ It hasn’t had the useful updates that the plain C library has had yet, but it’s there if you need it :)
It’s 4 wire SPI, true, but realistically, you’ll have the reset and interrupt pins connected as well.
The main difference/advantage of this vs an xbee, for instance, is the price, but also SPI instead of uart, so you can go much much faster. It’s pretty much bare 802.15.4 though, no magic IO line passing or ADCs. (Did I mention how much cheaper they are? Or that they are on breadboard friendly 2.54mm pitch pins?)