I wrote a GPL licensed layout manager (https://golden-layout.com/) that also comes with commercial licenses. It's been out for three months now and seems to appeal to financial institutions. Revenue is ok, especially since most sales are the more expensive (399 GBP) multi domain license, but a lot of the bigger customers don't want to just purchase it through the website, but rather enter into a more bespoke contract which comes with some overhead.
Actually, all I did was post it on hackernews. This generated a lot of initial momentum, but page views are now slowly declining, so I guess I need to find new channels to promote it.
cheers, it's a side project, but I'm also going to try my luck at starting a start-up this year and this is one of the components it needs - so its killing two birds with one stone. Revenue was between 1600 and 1000 GBP a month so far - although after just two and a half months this isn't exactly a representative sample.
