Unix and C are the ultimate computer viruses. ["The Rise of Worse is Better" by Richard P. Gabriel, included in "The UNIX-HATERS Handbook"]

Edit: thanks pjmlp. With so many name changes I forgot that IBM still had an alternative OS for small computers. I imagined that maybe there were still other mainframe systems, but I was too lazy to check...

Far as surviving ones, Burroughs MCP and GCOS are still around. BeOS is being cloned by Haiku. Amigas are still around with MorphOS being good. eComstation maintains OS/2. The THEOS OS and GEM(?) window system still exist. Plan 9 of course. GenodeOS continues microkernel-style tradition. JX continues language-style security trend. Oberon legacy last iterated as A2 Bluebottle OS.

So, there's several I recall.

Essentially it. Each on my list were innovative in their capabilities with some capabilities still missing from UNIX. They just didn't have economic and social momentum behind them. Far as FreeDOS, I left it off because it wasn't really innovative or worth copying. I'd take UNIX or Oberon over DOS any day. Maybe eCOS given its innovation was being highly and easily configurable.

http://ecos.sourceware.org/about.html

Yet, each contributed architectural or feature innovations that are worth considering or copying to this day. Some you still can't buy on the market: Burrough's hardware security or Genera LISP's development capabilities. Some FOSS hasn't quite caught up to: BeOS's amazing, consistent, desktop experience; OpenVMS's bulletproof clustering and other availability features [1]; OS/app security of KeyKOS or EROS; low 0-days in kernel code due to use of high-level language with extra type or memory safety. So, they still kick UNIX and Windows ass in numerous attributes. Ironically, it's Microsoft and Windows trying to copy as many techniques as possible from old systems rather than UNIX. Their quality and security levels have skyrocketed vs Dark Ages of Microsoft. UNIX (or alternatives) have plenty room to grow by using differentiators like on my list.

Note: I especially encourage you to carefully read the Genera LISP machine page. Some points are obviously old news or even laughable today ("has TCP/IP"). 8-13 for debugging down to OS level and 16 are a pretty badass combo you ain't getting with UNIX, C, and GCC. ;)

[1] Maybe Amazon Web Services would've gone down less if they, instead of UNIX, were running on VMS boxes known for individual uptime of 3-5 years and cluster uptime of up to 17 years in hands of average sysadmins. Ya think? :)

However, I imagine that if I seat myself in front of a 2016's fresh installation of Aix, HP-UX, Solaris, Tru64... I will struggle to find any major difference from a 2006 installation, the last time I used any of them.

Far as Linux, Ubuntu with its software-center, Flash, VLC, and so on are much different than my early experience with Caldera OpenLinux on a Pentium 2. Which would've looked like shit with almost no apps or features had it not bricked that machine during install. ;)

So, they're not very innovative but have had huge improvements that totally change the user-experience. I mean, certain things are similar or the same especially on terminal end. Yet, we can't pretend like UNIX has sat still. It's just still not fixing its worst issues or learning from prior work as effectively as it could.

As for the desktop, yeah the experience has improved, but still no proper GUI stack in place, all is built on top of X architecture.

Nothing compared to the work done at Xerox, DEC/Olivetti or even what Microsoft does at MSR.

I came to me thinking how similar the coding experience in Mac OS X, Android and Windows or the whole OS stack is to the way I experienced Oberon back in the day.

Yes Mac based OSes and Android have a UNIX kernel, but when using the official APIs for applications, one would hardly notice it.

I've been saying for a while that a group needs to do this for one of the BSD's. Not just put KDE or Gnome on one but seriously reengineer the GUI, sounds, graphics, admin controls, and package mgmt. Smooth integration with high usability and good efficiency like Macs. Closest I've seen was Mint but had to ditch it for security reasons.