Yes, it's possible to grow a list without any existing audience, any hacks, ads or tools.
A few hours ago I got my 200nd subscriber, just 2 weeks after I launched my project.
To celebrate I opened the comments on any post at
https://goodmarketingstuffs.com. It'll be better to centralise all discussions I have across Linkedin, Twitter, Reddit, Producthunt and so.
It's a bit old-school but it does feel right.