As a retired engineer, I find robotics an interesting and challenging  hobby.  I have a number of experimental robot platforms which can utilize sensors  to monitor the environment and  serve as input to a microprocessor which in turn commands an output in the form of a servo motor or a stepping motor.

• The ER1 is a fairly sophisticated robot platform which was sold by Evolution Robotics, Inc.   The ER1 consists of a sturdy aluminum frame with one or more video cameras for input, a control box and stepping motor wheels which could respond to either the video signal or up to sixteen analog to digital inputs from sensors.   It could be programmed in Java, Python and several other lesser known languages. Unfortunately,the ER1 was fairly expensive and required a laptop computer for its control.  It had a limited market, so Evolution Robotics quit selling or supporting this platform. 
•  The Lego Mindstorms  RCX is a robot brain.  Lego bricks are used to build the structure of the robot.  The RCX can be programmed in a subset of the "C" programming language called "Not Quite C (NQC)" or a subset of the Java programming language called "Lejos".  The RCX can utilize up to three sensors on the input and can control three outputs.  These outputs are  usually motors.   The RCX is being superseded by a new Mindstorms robot  called "NXT".