I wouldn't know where to start but a robot that could interact with Autistic children, play games with them, use text to speech to tell them stories and help teach social skills would be a fun robot to build.
By Lemon
Other robots from Synthiam community

Steve70x7's Robot Albert E
Hi Everyone, Here is some info about Robot Albert E, my 2nd robotics project. Robot Albert E is a life-sized head in a...

Ezang's My New Metal Robot With Voice Commands...
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Ianmbrick's Project To Link A Microsoft Kinect Xbox 360...
Overview ------------- In this post I present a project that I set up to link a Microsoft Kinect Xbox 360 sensor with...