This app was mentioned in 1 comment, with an average of 4.00 upvotes
I used my desktop dev skills to create a product which I used my web dev skills to promote. In 5 years I've made about $25.000 on it, so it's never been a sustainable income.
Most of the time I've had a full time job keeping my own products side projects, except for 9 months in 2011 when I "took the leap" and made an Android game. Pro tip: Stick with the corporate market. Games are hard.
It's been fun though, although the product mentioned first has peeked a long time ago. I'm now only doing the minimum effort keeping it alive for my loyal customers (you can come a far way by being nice and responsive to support mails).