Quicksilver MX Sprint
I built this airplane in 13 days from crate-to-air. It had a Rotax 503 motor and I put 80 hours and 342 landings on it. It has a steerable nosewheel.
The single-seat Quicksilver not only complies with the US FAR 103 Ultralight Vehicles rules, but was in fact the aircraft around which the rules were developed. The Quicksilver was the most popular ultralight aircraft design when the regulations were first drafted in the early 1980s.
See my video of the preflight and flight here.