As in software that’s licensed under a open source copyleft license, but costs money to run that’s beyond an optional request for a donation. I can see this happening with libre hardware since it still costs money to manufacture even if the design is free, but with software, wouldn’t someone immediately fork the project to remove the payment requirement?
Plenty! But it’s not something you pay to download. Organizations ranging from large companies, FOSS companies like SuSE/RedHat/Canonical, down to individual contractors develop https://en.wikipedia.org/wiki/Custom_software and often contribute to FOSS in the process.
For example look for “employers” “by lines changed” in https://lwn.net/Articles/839772/