Might not be the same thing, but I had/have built (a) project(s) that I began with the dreams of someday monetizing, but later realized, maybe I shouldn't, couldn't figure out how to charge for it, or didn't see a need of why anyone would pay to use it, and thus, ended up just keeping it as a "free platform".
I'm not upset about the decisions I've made for keeping my projects free, as if anything, they have taught me a lot, and I tend to use what I learned from them for future projects. In most cases, I end up turning on an Analytics feature and studying it, in order to understand the behavior of my users, and exactly what they are using it for and why, so that I can harness that into ideas for future projects.
Two projects like this were a blog I run called Confessions of the Professions ( http://www.confessionsoftheprofessions.com ). This website was created in order to solicit rants and raves from people about their jobs, careers, and their workplace. While I wouldn't call it a complete failure or complete success, as it has been monetized and makes money through ads, I would've loved to figured out a way to bring in revenue and make it a full time job.
The reason I say success and failure: It goes viral for days and weeks at a time, sometimes receiving over 10,000 visitors a day, while other days, it normally gets its average of about 1,000, though it could be worse. Sometimes, I cannot fully recognize the fact that I began with just Googlebot, my mom, and girlfriend as my visitors, and yet I continue to receive hundreds of emails a year with contributions and people thanking me. I even had a teacher from an elementary class full of students using some of the articles for their school project and thanked me so much for creating the website.
Confessions remains an ongoing project.. I'm always writing articles or receiving them from other people and getting them ready for the website, so I'd say I spent a good 2 years passionate about it and into it, hours and hours a day. I've since limited myself to no more than 1 hour per day on it. Occasionally 2 hours if writing an article.
For the other project, MyPost ( https://mypost.io ) is a web page creation platform that allows anyone to create a page with very little knowledge of HTML or CSS in seconds, or they can completely customize their page with HTML and CSS as they see fit. And there is soo much that people can do with it. I created it for a number of different reasons as well, including as an educational tool for people to learn what it was like to code. Social media has catered to the population so much that while everyone "can use social media and the Internet", far fewer can claim to hit the "View Source" button and actually understand all that makes a website what it is.
As for charging for this, I never could figure it out and hoped to one day just put ads on the website, but ended up scratching this idea, as the ads were just too annoying, even for me. I can tolerate some ad popups, but I created the platform to offer people an experience, not an annoyance. It is this project that taught me a lot about databases and a lot about what people want on the Internet, and that is: an easy way to gain exposure. I have plans for a another project that helps people to do that, similar to ProductHunt and Hacker News.
The time I spent on this was about 3 months initially and then another 2 months just making some changes, fixing things, creating samples, etc.
I would love to quit my day job and just work on side projects and monetize them.. as I'm sure many of us would, but I have yet to get to that point completely. I do have a few projects I built completely with monetization in mind, and while there is a free version of those products, I built them as a subscription-based platform. I also have a few other projects in mind that I have no intentions of charging for.... for some projects, it is more about gaining exposure and recognition for me.