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?
Yeah, most FOSS companies also offer their specific platform for their software for a price. Depending on the complexity of self-hosting it can be much cheaper to just buy access to the platform
Additionally, the source code of free software only needs to be released to your users, not necessarily the general public. This means that if you have a niche client who doesn’t want to write their own software, it can be a steady income stream, and you can set it up so they have to be a customer to be an initial user