What can be used only using BSD, MIT, Apache licenses? And what from the GPL-licensed products is safe to use to produce and sell own closed source products (e.g. where the exception to GPL exists for just linking the libraries or similar)?
Edit1: Long term dangers/costs of depending on the technologies that need commercial licenses like Oracle’s are also important.
Edit2: And additionally, just as an old example, once I’ve considered using Berkeley DB in the closed source product (before some of the current alternatives were available), and my interaction with Oracle proved that only a bigger corporation could fund that. For a library which was already open source, but owned by Oracle. It's not that I'm in the "I don't want to pay for anything" camp -- I'm simply having a perspective of a small player. And about small players Oracle couldn't care less. However, the significant changes very often come at that level of cheapness and overhead, most of technologies would be still not widely accepted otherwise.