Yes.
NetBSD was created in 1993.
Windows 2000/XP/2003/Vista/7Linux (kernel 2.2 and higher)Mac OS XFreeBSD/NetBSD/OpenBSD
Unix versions are the biggest competitors of Microsoft OS. Few of them are:SCO UnixRed Hat Linux & Red Hat Enterprise Linux (Red Hat)Suse Linux (Novell)HP-Unix (HP)AIX (IBM)Solaris (Sun MicroSystems)BSD/OS (Wind River)CLIX (Intergraph Corporation)True 64 Unix (Compaq)SPAEC 64/OS (HAL)MacOS X Server (Apple)NetBSD (NetBSD)OpenBSD (OpenBSD)OpenLinux (Caldera Systems)
DOSBox is cross-platform. It runs on Windows, Linux, Mac OS X, BeOS, FreeBSD, NetBSD, OpenBSD, OS/2, Palm OS, Sony PSP, Nintendo Wii, and GP32x. It is designed to be easily portable, and thus can probably be run on other besides these.
NetBSD is a derivative of BSD created in 1993. It is best known for being highly stable and being easily portable across multiple architectures.
NetBSD is a free, open-source, unix like, multi-platform operating system descended from Berkeley Software Distribution (BSD) and based on 4.4BSD Lite.
There is no such thing as "PC OS." The IBM PC and compatibles are host to a variety of operating systems, including MS-DOS, Windows, Linux, Chrome, OS/2, FreeBSD, NetBSD, OpenBSD, Solaris, BeOS, SkyOS, Syllable, CP/M, DR-DOS, FreeDOS, SCO Unix, AROS, KollibriOS, Haiku, Native Oberon, Minix, MenuetOS, QNX, VisiCorp Visi On, and probably a dozen more I probably forgot.
http://www.tux.org/~bball/z50/
Dozens of operating systems have (true) multi-user support. The most notable include: Windows (NT/2000/XP/Vista) Mac OS X Linux FreeBSD NetBSD OpenBSD Solaris Plan 9 QNX BeOS GNU HURD AIX VMS HP-UX IRIX Tru64 VxWorks
FreeBSD: v3.3.0 Linux OpenBSD NetBSD Solaris: v3.3.0 Mac OS X v10.2: up to v1.1.2 Mac OS X v10.3: up to v2.1 Mac OS X v10.4-v10.5 (PowerPC): up to v3.4.0 Mac OS X v10.4-v10.7 (Intel): v3.4.0 Windows 95: up to v1.1.5 Windows NT 4.0 Service Pack 6 - up to v2.0.1 Windows 98 - Windows ME: up to v2.4.3 Windows 2000 - Windows 7: v3.3 (Tablet PC input is not supported) OS/2 and eComStation: up to v3.2.0 IRIX (mips4): up to v1.0.3
* Windows 95 (only in later OEM releases) * Windows NT 4 (only with a third party driver) * Windows 98 * Windows Me * Windows 2000 * Windows XP * Windows Server 2003 * Windows Vista * Windows Server 2008 * Windows 7 * Windows Server 2008 R2 * Most Linux distributions * Mac OS 9 * Mac OS X * FreeBSD * NetBSD * OpenBSD * FreeDOS
Windows 7, Vista, XP Home/Pro, 2000, Server 2003, Server 2008 Linux kernel 2.6 has native ipsec support, so about all modern Linux versions will support it OpenBSD, NetBSD, FreeBSD, and Dragonfly BSD currently support it Mac OS X