Lets you control Lego Mindstorms NXT robots from an Android phone via Bluetooth. Protocol is <a href="http://mindstorms.lego.com/en-us/support/files/default.aspx">documented</a> on Lego website. The official <a href="https://github.com/NXT/LEGO-MINDSTORMS-MINDdroid">MINDdroid</a> app is also free software.