Electric motor attached to a wheel attached to a handlebar.  Does this look like fun or what.

Rollerblading always seems like so much fun when we see people zipping through the Park, but the whole
self-propulsion thing kind of turns of off, which is why we’ve been waiting for a device like the Easy-Glider.
Basically an electric motor attached to a wheel attached to a handlebar, the Swiss-made Easy-Glider Deluxe propels
whatever its towing with 380 watts of eco-friendly power, and even recharges itself while cruising downhill (probably
not fully). The less-athletic among us can decide to forgo the ‘blades or skateboard altogether and step up to what
we’ll call the "touring package," which attaches a small wheeled footbridge to your ride. Prices range from a
steep $1,025 for the Standard without footbridge to an even steeper $1,315 for the Deluxe with, not to mention the hefty
shipping charge you’ll have to pay to import one from Switzerland.

More here.