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

Robotdude's Bad Jokes
So LieutenantCommander Data the customers greeting droid is awesome! He is still fully functional for two years (24/7)...

Cardboardhacker's Rover Ad
This is the thread for my current project Dewy. He is a tall robot that uses RAD parts and models a omnibot in a way....

Clode's The Canadian Mars Explorer :-)
New project to work on this winter Canaxplorer. The Canadian Mars Explorer. This rover is controlled by EZ-B with cam,...