Marvell, a California based company, has built a Linux computer which is about the same size as an electrical plug.
The product named "SheevaPlug" is not just another mobile devive running Linux. It is a new class of computers concieved very recently called Plug Computer, which provides desktop class performance.
As Marvell puts it:
The SheevaPlug is a development platform, targeted for use as a plug computer, and designed to run network-based software services.
The SheevaPlug uses an embedded Marvell Sheeva™ CPU core running at 1.2 GHz and has 512MB of DRAM and 512MB of Flash memory. The devive connects using Gigabit Ethernet socket and is targeted as a replacement for PC-based home server for many applications like media server, back-up services, file sharing and remote access. A USB 2.0 port is also provided for connecting other peripherals. It consumes only about 5 Watts of power.
Where the SheevaPlug scores over a traditional PC-based home server is that it only uses a tenth of the power consumed by a PC-based server, making it not only a greener option but also a cheaper one in the long run.
A USB-based debug connection is also included to enable simple debugging and reprogramming.
And lastly, this device comes for $99 which is quite cheap.
If you want to check out the Marvell page for this device, click here. A good analysis of how the entire thing works can be found here.