I don't think the point is how common it is, it's about a organizational model.
Linux and Postgres are not reliant on any one commercial entity being successful for their continued existence. Even many of the maintainers are not reliant: if the company/foundation Linus Torvalds is working for at the moment has to close down, someone else will pay him to keep working on Linux. And even if he couldn't personally work on Linux anymore, there are enough other people in a similar position that Linux won't die.
I'm sure there are many much smaller and more obscure projects in a similar boat, especially in academia. If the code is not dependent on a single entity for maintenance, both in terms of someone knowing it and in terms of someone paying for it, then it will naturally thrive for a very long time.
Linux and Postgres are not reliant on any one commercial entity being successful for their continued existence. Even many of the maintainers are not reliant: if the company/foundation Linus Torvalds is working for at the moment has to close down, someone else will pay him to keep working on Linux. And even if he couldn't personally work on Linux anymore, there are enough other people in a similar position that Linux won't die.
I'm sure there are many much smaller and more obscure projects in a similar boat, especially in academia. If the code is not dependent on a single entity for maintenance, both in terms of someone knowing it and in terms of someone paying for it, then it will naturally thrive for a very long time.