The Contiki operating system allows tiny wireless battery-operated devices to communicate using IPv6 – a concept known as the Internet of Things. The Contiki team has just released Contiki 2.5, which brings ContikiRPL, the new default low-power IPv6 routing protocol, and ContikiMAC, which allows nodes to keep their radios off more than 99% of the time yet communicate with each other using wireless multi-hop networking. The Contiki Wiki has more information on Contiki.
… not nearly as cool as it used to be. Contiki 1.x was awesome: a multitasking OS with GUI and TCP/IP support that ran on things like C64s and Apple IIs. 2.x turned into something that while more “useful” (a tiny OS for deeply embedded uses like sensors and such) than 1.x, lacked many cool features like the GUI layer and the support for various home computers.