This has got to be one of the lowest-cost and simplest embedded Linux boards out there:

It’s the Carambola 2 by 8devices.com:

The 28 x 38 mm (!) bare board is €19 excl VAT and shipping, and the development bundle (as shown above) is €33. The latter has a Carambola2 permanently soldered onto it, with 2 Ethernet ports, a slave USB / console / power port, a USB host port, a WiFi chip antenna (which is no longer on the base board, unlike the original Carambola), and a switching power supply to generate 3.3V from the USB’s 5V.

The processor is a MIPS-based Atheros chip, and with 64 MB ram and 11 MB of available flash space, there is ample room to pre-populate this board with a lot of files and software.

The convenience of the development setup, is that it includes an FTDI chip, so it comes up as a USB serial connection – you just need to find out what port it’s on, connect to it at 115200 baud via a terminal utility such as “screen” on Mac or Linux, and you’ll be hacking around in OpenWrt Linux in no time.

Note that this setup is very different from a Raspberry Pi: MIPS ≠ ARM, for one. The RPi has a lot more performance and RAM, has hardware floating point, and is more like a complete (portable) computer with its HDMI video out port. The benefit of the Carambola 2 is its built-in WiFi, built-in flash, and its low power – more on that tomorrow.