@WoodshopHandman @Myles @doctorsex @sickburnbro Things that are highly regulated, so no access to the market on a small scale, or illegal entirely:
Guns
Cars/engines
Alternative building technology
Non-industrial food and beverage
Non fcc compliant communications tech
Cryptography


Things like that (each item in that list may our may not be guy I know)

But mostly it's time and money, not passion that's lacking, at least in my limited experience