Even if all software is open-source (which I doubt), that does not mean that nobody can earn money from it; there are still ways to earn money, too.

Others:

MS-DOS / PC-DOS -- FreeDOS

ZZT -- ZZT (the source code was rewritten to produce the same executable file; the original source code was not made available)

MESH:Hero Hearts -- Free Hero Mesh

Windows NT -- ReactOS

BTRON -- B-Free (incomplete and seems to be abandoned?)

(And, the above are definitely not all)