RobotBits.co.uk has begun selling an open source mobile robotics kit from Frindo.org available with an Arduino Duo, or as an under-$100 model that lets you add your own Arduino and/or Raspberry Pi. The Frindo robotics platform, which appears to be about 100mm in diameter, is billed as being more robust than most low-cost educational robots, and is optionally available with a motor controller board and sensor bundle.