Ask HN: You built and they just came?
Are there any stories when you went ahead and just built something, did minimal (or no) marketing and users just came?
Before that, I made a website called the South Park Kenny Translator [1] and I don't recall doing any promotion at all, besides it being on the same domain as my Photoshop plugins. It's been around for almost 20 years now and even landed me an interview on BBC Radio. The Kenny Translator is inherently viral though: the whole point is sending Kenny-encoded messages to friends.
Nowadays I'd be much more proactive about marketing. My current Indie Conference [2] side project went nowhere for a couple of years, but suddenly got a spike of subscribers when I mentioned it in a reply here on HN last month. It wasn't intended as deliberate marketing, but it had more impact than 2+ years of nothing but hoping the Google gods would look favorably upon me.
Your product has to be outstandingly super good to gather users without any marketing.
I once ran a p2p site called flashseed. The basic premise was that it was a torrent tracker that solved the two major failings of bittorrent - initial seeding and incomplete swarms, by hosting a static copy of the file.
I posted it on a forum, but due to the ill-conceived name people thought it was a free seedbox rather than a tracker. It blew up overnight and crashed the server. 99% of the files uploaded turned out to be pirated movies and TV shows. At the time isohunt was being sued and the legality of the site was unclear, even if I did comply with DMCA. After some thought I decided it wasn't worth the effort, and let it die a natural death...
If I were to do it again I'd probably make it invite-only