None of those require any personal investment. I think GP meant something that takes a lot of your personal time to do, while staying unprofitable no matter th

None of those require any personal investment. I think GP meant something that takes a lot of your personal time to do, while staying unprofitable no matter the skill level. For example, ROM hacks and emulators: they're difficult and time-consuming to create, and they can't be monetized for legal reasons.