Here's a new project that a few of us are working on in the UKhttp://wiki.hackspace.org.uk/wiki/Project:Nanode
It's an open hardware/open source, low cost platform on which to develop smart sensor and network applications.
It's easy to make from a kit costing about £22 (25 euros, US$ 40), and ideal for hackspaces, schools, colleges, hobbyists etc.
For more information check the London Hackspace Wiki for regular updates or check Twitter for #nanode
If you want more details, or want to make a batch of pcbs from the design files for local distribution outside the UK - please contact @monsonite on Twitter.