Like you Alex, I love dreaming up new projects, but have a similarly low conversion rate - although I definitely do build some of them
I've done a little preparatory work on the idea of a very large nocturnal solar reflector that could orbit the earth and reflect sunlight down to my personal power station at night.
it still needs a lot of work, and the power is currently very low,but here's a picture of me adjusting the prototype reflector. Just kidding of course.
However, I did build a weed extractor that actually worked
We had a plague of dandelions around the house - 20,000 plus. I began digging them out by hand but then designed and built the device in the other pictures. The idea is to push the forked plate into the ground so that it grips the sturdy taproot of the dandelion. You then use the hinged part to drop it down onto the fulcrum beneath. Then a firm downward press on the handle shoots the offending weed into the air.
It actually works! (Note the startled expression on the face of the rising dandelion in the last pic). Sadly it wasn't any quicker than digging them out by hand, although it was a little easier on the geriatric knees - and lot of fun to use. You could fire a dandelion up to about waist height. I spent some happy times laughing at the results, but still eventually dug them all out with a trowel and bucket.