[bitwize]

While Apple was faffing about with Taligent and Copland, Microsoft shipped something that provided preemptive multitasking and memory isolation for 32-bit apps.

Windows 95 was a collection of hacks that never should've worked but it put Apple behind the 8 ball to bring its OS tech into the present.

[Taniwha]

Apple also shipped A/UX which did all that

[wmf]

And was so expensive no one cared.

[rbanffy]

And this is probably the greatest inhibitor Unix had for its adoption.

[switchbak]

They also shipped the Lisa prior to that, which also had protected memory and pre-emptive multitasking. This died for other reasons however (too expensive, upstaged by the mac, etc).

[Angostura]

Oh, I rather liked OpenDOC.