I've started a few different companies, built and launched a dozen or so things, and learned a lot. Here are a few!
32Best (shut down)
Crawled real estate agent reviews across a dozen review sites and social media platforms to derive a score and identify the best real estate agents in each market.
Notesurf (shut down)
A marketplace for college students to buy and sell class notes, study guides, etc. It turns out colleges consider notes students take their IP, so don't recommend this. :)