Sphero is a robotic ball that can be steered with a remote control or programmed. In either case, you interact with Sphero using a mobile device. The Star Wars BB8 version has further increased its popularity.
The Lightning Lab has sample lessons from teachers who use Sphero to teach everything from art to programming to literature to science. Figuring out how to construct a cart for it to pull is a neat challenge, and the video here shows the Sphero Rig, which I designed and 3D printed. The Sphero is pretty durable and is waterproof.
@SpheroEdu is a good channel of information.
Here are the links for my 3D design:
A quick introduction