I disagree with the original post that implies BeOS was better than NeXT. There are a lot of really useful, cool things in NeXT that are not appreciated by the masses and forgotten with time. All the new iOS developers don't know how much history/heritage their stuff is built on.
For example, fat binaries are so incredibly useful and elegant. While Mac easily transitioned from PowerPC to Intel, then 32-bit to 64-bit, and now all all the different ARM architectures on iOS by using fat binaries, all the other platforms are a mess with just their 32-bit to 64-bit transition partly because the need to differentiate between two different architectures on the file system breaks most tool chains. (Not to mention that it confuses the hell out of users about which version they need to download.)
Linux had their chance with Icculus's FatELF patch and they rejected it. Only years later after great suffering is some of the Linux community starting to think maybe FatELF was a good idea after all. Too bad our 64-bit migration is almost over. But Android still really could benefit from this because that system is a mess that looks like it will need to deal with multiple architectures indefinitely.
I also agree on Be. While I used BeOS (even got to play with it on a BeBox) and was impressed by it, NeXT was the better system. Oh my, networking was a mess in BeOS, and I'm not sure they would have ever gotten full multi-user support.
As a youngster, I pined for NeXT after playing with one at a university lab. I still marvel that we now carry NeXT workstations around I our pockets.
I really wish the Linux / BSD communities had rallied around GNUStep. Would have been nice to see how two implementations coevolved.
I'm still saddened that GNUStep never went anywhere. I still find GTK/Gnome/Qt/KDE wonky for a lot of basic things like copy-and-paste and drag-and-drop.
My wildest dreams hope to see a re-emergence of something like GNUStep, but this time be driven by all the new interest in Swift.
There was an attempt to get Window Maker back in the limelight last year. Not sure where this has gone...