Earlier quoted context omitted.
Startups obviously. Less obviously look for "SBIR" shops if you're ok with a little bit of weird gov contracting overhead.
Startups don't stay small though. They're aiming to get really big or have some kind of big exit in a hurry. Some of them are a lot of fun, some stay good even as they grow, others turn into depressing places to work.
Maybe you get lucky and find a labor-of-love kinda place where someone is just trying to be really good at making one type of thing (highly niche products) but a better bet is to just find a comfy place, stay there a few years and help them get bigger, then leave and repeat.