Wankel rotary engine. Invented by a guy who then got buy in from Mazda.
Metal Storm firearms with no moving parts. Invented by a backyard guy who turned it into a corporation.
At the bottom end of the scale is the upside down tomato plant beloved of TV huckster shows. May not be a world-beating idea, but someone had to think of it, develop it, make a prototype, pitch it to someone who had the resources to come up with distribution, etc.
There are a bajillion of these things. I saw a plastic device designed to make folding shirts easier. And there are stacks of funny little food preparation gadgets too. The corkscrew that you pump like a slot machine without having to twist the damn thing. These can only have been invented by small time guys who managed to leverage the idea up to the point of production.
I once met an inventor who invented a bike whose foot cranks did not turn in a circle. They were geared and engineered to be pressed up and down rather than round and round. The idea was that that motion more closely matched ordinary biomechical walking than did the round and round motion and was therefore “better”. He was very proud of his invention and had put huge amounts of work into it. The huge problem seemed to be that whereas a simple wheel arrangement associated with the pedals serves a conventional bike well enough, the machinery necessary to convert an up-and-down motion into rotary energy for the driving wheels was so heavy that the whole project was pointless, what with weight being kind of a Big Deal in bikes. And the power transfer wasn’t even like it is with conventional bikes - at the top and bottom of the stroke, the effort involved seemed harder than during the middle part.
The real problem for inventors is breaking into what is now a very sophisticated market. An inventor might be a genius of the level of Edison, but without the finance and without the business and marketing skills necessary to convert the idea into reality and put one in every household it is going nowhere. The finance issue is not trivial, and nor is the organisation of distribution networks, inventory, manufacturing runs, being careful not to overestimate nor underestimate the market for the product, etc.
As a result, inventors tend not to make as much money out of even successful ideas as one might naively think. It’s the guys who take the financial risk by stumping up the cash who take the rewards, in the traditional capitalist manner. The inventor has usually had to compromise his rights severely (by diluting his share in the profits) in order to get some person or company on board who can do all that other stuff.