An OS where the source code isn't released to the public. Windows and Mac are 2 examples.
There are many open-source operating systems. They include: Systems based on the Linux kernel (Ubuntu, Debian, RHEL, Fedora) FreeBSD NetBSD OpenBSD ReactOS Haiku AROS FreeDOS GNU HURD Darwin (the...
Linux and FreeBSD are 2 examples
Linux NetBSD FreeBSD OpenBSD Plan 9 LUnix Darwin
Microsoft: MS-DOS WindowsApple: MacintoshUnix-based: Red-Hat Linux UbuntuGoogle: Chromium