Heres a sampling:
Be: Apple discussed buying this OS company in 1996 but instead opted to acquire NeXT in 1997. Be was founded by Apple veteran Jean-Louis Gassée.
Copland: A Mac OS upgrade under development from 1994 to 1996. It became one of Apples biggest software disasters. Copland consumed $250 million in R&D in 1996 and never shipped.
Pink: An OS project launched in 1987, Pink was the doomed precursor to Taligent.
Raptor: A 1993 project to head off Windows 95. Bureaucracy killed the effort.
Star Trek: A secret 1992 alliance between Apple, Novell and Intel to put Mac OS on Intel hardware. The project died in mid-1993.
Taligent: An object-oriented OS first launched as Pink. IBM later lent a hand in the debacle. Taligent ultimately became a tools company that died in 1995.
Windows NT: Apple quietly demonstrated Windows NT on a PowerMac in the mid-1990s during the Comdex trade show in Las Vegas. Rumors swirled that Apple wanted to deliver NT-based servers but nothing ever became of the project.
Sources: Sm@rt Partner research; "Apple," by Jim Calton; "The Second Coming of Steve Jobs," by Alan Deutschman