Matt Brown - security researcher and bug bounty hunter

Robert Murray Smith - general mechanical engineering tinkering, lots to learn

TheCod3r - console and other electronic repairs

Wesley Kagan - builds cars but is just an overall genius and entertaining

Joe Grand - hacker, genius

There are more popular/sometimes better people and channels in each genre but I've stuck to those with under 1 million sub's. I'll assume people like Colin Furze, Ben Eater, Computerphile are already too well known for this thread

Bobby Fingers. He makes diaramas of weird things and then buries them in the woods for people to find. Doesn't make videos too often but they're hilarious.

Kyle the Scott. A Scottish cisman with a kinda effeminate voice who once did a dramatic shirt rip to prove he is in fact cis, in the middle of a half hour essay about why it shouldn't even matter and "transvestigations" are bullshit.

But his normal schtick is media criticism, covering franchises like Star Wars, Halo, and Assassin's Creed. They're just genuinely good reviews that aren't afraid to get into the politics where appropriate (including explicitly rejecting some of the more popular bigoted takes) but honestly feel it's about the way that particular lens affects the media, rather than being an end into itself.

twoodfrd - the guy repairs guitars with his soothing voice and lots of technicial knowledge

A really tiny channel I like is Don't Look East. Currently less than 3000 subscribers and most videos just get a few hundred views. He does unscripted travel vlogs about rarely visited destinations, mostly in Asia and Eastern Europe. For example he recently travelled the entire Thailand/Myanmar border by motorcycle.

Aussie Wood Shed