I have been running a search engine for online courses for the last 15 years: https://www.classcentral.com/

The current catalog covers 100+ providers, 1000+ universities, and 250,000+ courses.

Originally a weekend side project that I first shared with the world here on HN itself on Nov 29, 2011 [1]. Currently bootstrapped and profitable.

https://news.ycombinator.com/item?id=3288775#3289393