WAmigaOS
WAROS Research Operating System
WBlackBerry 10
WFreeRTOS
WGenode
WGhost (operating system)
WGNU
WGNU Hurd
WHelenOS
WMac OS 8
WMeiko Scientific
WMINIX
WOS2000
WPhantom OS
WPikeOS
WPowerUP (accelerator)
WQNX
WRedox (operating system)
WRIOT (operating system)
WSharpOS
WSingularity (operating system)
WSymbian