The Zolertia Z1 is a modernized replacement for the Telos B, using a more modern MSP430 and a different USB chip but being otherwise nearly identical. Most importantly, the Z1 is available for order at the Zolertia website.
Build and flash firmware with the following commands. The $board variable must be set whenever the client is used, and the device will not function without it.
export board=z1 make clean install goodfet.ccspi info goodfet.spiflash info
Schematics and documentation can be found at http://www.zolertia.com/ti along with ordering information and expansion boards.
The Z1 has only been tested with the GoodFET in Linux. Mac and Windows compatibility have not yet been verified.
A few nifty examples for the related Telos B board are covered in the article GoodFET on the TelosB, TMote Sky. Specifically, the device is good for 802.15.4 packet sniffing and injection, as well as for the quick prototyping of new applications. Scapy integration also allows for packet dissection.