So much you can't even have a directory for them.
Would you rather use an open-source project that has 2000 open issues and only 1–2 updates per year, where developers haven't responded in months and have no incentive to help you, or pay for the software, support the developers, and receive quick answers to your questions and even have your issues/bug reports addressed immediately?
Personally, even if I use open-source "free" software, I often donate to the developers, because I want that software to be maintained and improved, or even have my feature requests implemented.
Why are people so reluctant to pay for stuff they actually need/use and to support smaller businesses? It's not even about being selfish, because paying the developers actually will make your experience with the product better.