Well if you don't count my work as a teen mowing lawns, I tried to get a business going in photography (back when film was used, a light-sensitive chemical spread over a clear plastic), some weddings, some parties, some ads, some portraits but not enough to live on, so I went to technical school instead. (and used some student loan money to buy a telephoto zoom lens.)
About 15 years ago I tried my hand at a live recording & photography business, but found musicians - however talented - to be both flaky and lacking in cash. Now-adays everybody just uses a computer.
More recently I dabbled in hobby electronics, making pcb's that are to be used in other projects. A Kickstartr drive was successful, but my website (which is still there) is full of cobwebs and crickets. In spite of many marketing efforts and dollars, I suppose my stuff is just too expensive and not interesting enough. The only real profit I got from this particular business is that I also threw in electronic engineering/consulting, which makes it all profitable - but really it's just a part-time job with an old employer.
Never rebuilt a car in one project but changed my share of batteries, tires, fuel pumps, radiators, windows, headlights, fuses, hoses, radios, wiper blades...that I feel like I did!
In electronics though, I've taken on many rather ambitious projects at home, such as an analog synthesizer, digital synthesizer, MIDI processor, rhythm generator, DMX light controller...My work stuff of course I can't talk about too much, but those were seriously extreme in complexity and generally my own ideas (as an electronic manufacturing test engineer).
I still don't know how to use my phone though.