These are USB I2C/UART/GPIO bridges which can achieve 115200 baud.

Since they are available as a dual in-line package they are very easy to utilise.

The MCP2221 can be used on a breadboard like this.

A simple utility named Dougal has been written to query the MCP2221 and also demonstrate how to bit-bang the GPIOs.

hg clone http://hg.kewl.org/pub/Dougal
cd Dougal/src
make
sudo ./mcp2221 -b

Data-sheet