Yourbrowser.is

Sold via Flippa to a Latvian company.

It took a few years, because Flippa buyers are looking for businesses (website with traction - paying users, income) and Yourbrowser.is was listed as a website and a brand to be marketed, practically from scratch.

After being featured on Product Hunt and questions asked about a commercial version, a PRO Account has been introduced.
The free account remained fully functional, only some new features have been added (more customization options, Internet connection speed measuring, API).

Hunted by Eric WIllis (unplanned). Collected upvotes from some other popular Hunters.
Lots of valuble freeback collected, some users asked about a paid/professional version of the service.
Yourbrowser.is ended up "#2 Product of the Day".
https://www.producthunt.com/posts/your-browser-is

The website has been built to promote Super Monitoring (our main product).
The users (Web Developers and SaaS Support Agents) would send their custom checker URLs to their end-users together with Super Monitoring banners.
More about the concept here: https://www.supermonitoring.com/blog/hey-web-developer-please-send-our-ad-to-your-clients-thank-you/