Building an audience remains a difficult business task. It would be inspiring to hear success stories of products which launched with no following or prior audience.
Sold over 4,000 copies in the last 4 years - probably with help of luck (some people wrote reviews of the app) and also probably because people search for "porn hub" as "video hub".
https://videohubapp.com/ - and it's open source - https://github.com/whyboris/Video-Hub-App
Admittedly, I had a really hard time getting any traction for this project. Cold e-mailing media folks had some limited success but no sales impact. Same for HN and Product Hunt. But eventually Apple noticed and gave me a banner ad in the iPad App Store, which netted me about $10k overall.
Not exactly a success in absolute terms, but it made money with no prior audience.