Imma say, a lot of these ones: https://www.indiehackers.com/products

I would just look at successful bootstrapped startups that didn't have traction for 4+ years after the last pivot. E.g. Global Relay, Mailchimp, Bubble.is, ProfitWell, etc. And I wouldn't count something like Kickstartr, which took seven years to launch but only because the founder was non-technical.