| Acorn | AIX | Amiga | Apple | Atari | AtheOS | BeOS | BSD | BSD/OS |
Coherent | Compaq | Concurrent | Cygwin | Darwin | DG/UX | Digital |
Digital UNIX | DEC OSF/1 | DYNIX/ptx | Embedix | EMC | EPOC | FreeBSD |
Fujitsu | GNU Darwin | Guardian | HP | HP-UX | IBM | IRIX | Japanese |
JPerl | Linux | LynxOS | Mac OS | Mac OS X | Macintosh | MachTen | MinGW
| Minix | MiNT | MorphOS | MPE/iX | MS-DOS | MVS | NetBSD | NetWare |
NEWS-OS | NextStep | NonStop | NonStop-UX | Novell | ODT | Open UNIX |
OpenBSD | OpenVMS | OS/2 | OS/390 | OS/400 | OSF/1 | OSR | Plan 9 |
Pocket PC | PowerMAX | Psion | QNX | Reliant UNIX | RISCOS | SCO |
Sequent | SGI | Sharp | Siemens | SINIX | Solaris | SONY | Sun |
Stratus | Tandem Tru64 | Ultrix | UNIX | Unixware | U/WIN | VMS | VOS |
Win32 | WinCE | Windows 3.1 | Windows 95/98/Me/NT/2000/XP | z/OS | Inferno
| OS1100 | PalmOS | PRIMOS | Symbian | VxWorks |
The list above is copied from the home pages of CPAN. It is not complete. As you can see there is missing for example VIC20, COMMODORE C64, CP/M, CP/M+, MP/M, Menuet, OS/9, Symbian . . .
There is countless small 'operating systems' in the world. Every calculator and digital wristwatch has his own. I have myself made countless starting from a miniature 255 byte system for Z80 containing only three commands: load, send and run.