Unix vendor group formed by Apollo, HP, IBM, & DEC in 1988 in response to the Sun & AT&T announcement of their formation of Unix International to merge System V and SunOS to create System V Release 4 as the "new Unix standard." (Many joked that OSF actually stood for "Oppose Sun Forever".)
The original goal of OSF was to create the OSF/1 operating system, a merger of the Unixes of each of the founders on top of the Mach microkernel. Only DEC actually adopted the OSF/1 OS after it was finished, which it later renamed to Digital UNIX, then Tru64.
OSF also created the Motif GUI toolkit, DCE protocols, and after a reorganization that brought former arch-enemy Sun into the fold, the CDE desktop environment.
OSF merged with X/Open in 1996 to form The Open Group.