I and a few classmates in business school built a service to print people's top 5 instagram pics (top = #comments + #likes) every month and mail it to them as a nice physical keepsake. I was really flabbergasted that we couldn't get even 10 customers, we spend nearly $1,000 on ads before calling it quits (if we had had 10 customers we may have kept iterating but the setback was big enough to decide to just stop, and it only took a few weeks to build). Part of what was happening at the same time was the move towards stories, videos, and posts with multiples images, so it would have become way more complex than initially planned anyway and none of us were engineers.
The year before that I "invented" a mouthwash that was all powder based so you could travel with it despite travel liquid restrictions, the kickstarter campaign raised a decent amount but about a 1/3 shy of what it would have cost to place the minimum order with the packaging company (the power would be in tea bags), so I also nixed that but that was a fun side project