This Ask HN made for a great thread a few years ago [1].<p>To quote from the original "I've heard many of you love to create side projects for fun, but I also heard that few of them actually took off and grow into a profitable business. So feel free to list if you have any. Statistics will be welcomed as well!"<p>[1] https://news.ycombinator.com/item?id=1772224
www.lessonwell.com<p>I wouldn't say that this project of mine is "big" in the canonical sense, and it is only meagerly "profitable" by a loose interpretation of the word; but this has been a huge side project from my personal point of view. Essentially, I started this when I was teaching high school full-time and needed a better website for my calculus class. The "big" impact of this project is that it opened a door to a new career for me: I'm now a full-time software engineer and thus measure its profits on the order of my current salary, which is hugely significant to me.
<a href="http://grabaperch.com" rel="nofollow">http://grabaperch.com</a><p>Started life as a side project of our consulting business, is now all that we do. Not big as in making us millionaires big, but it's a profitable business. I wrote about a lot of the story of Perch and the stuff we learned in my book (another side project!) <a href="http://rachelandrew.co.uk/books/the-profitable-side-project" rel="nofollow">http://rachelandrew.co.uk/books/the-profitable-side-project</a>
<a href="https://www.expeditedssl.com" rel="nofollow">https://www.expeditedssl.com</a><p>A Heroku add-on I made at assist with SSL installation. Really deliberately chose to build in someone else's ecosystem where I wouldn't have so much to do myself.