Ramiferous Before exploring BSD, 10 years ago I was an happy OpenSolaris user.
I always loved it. Everything just worked out of the box, it had a good subpixel rendering inherited from Ubuntu, ZFS was integrated in the OS: TimeSlider in Nautilus was fantastic and the Boot Environments capability integrated in IPS was incredible.
If you run (Open)SUSE you'll notice their snapper tool. Well, OpenSolaris did even better by integrating the ZFS APIs into the package manager, instead of running a separate daemon. And they did it when the Linux community didn't even know what a CoW FS could do. They were dealing with the joke called BTRFS.
The only bad part of OpenSolaris was that IPS was really slow. But since Sun was tuning every part of the OS, I'm sure that they would deal with that as well.
Then Oracle bought Sun and the dream ended suddenly.
Illumos to be honest was always a joke.
Sun had the best engineers around but without a management with a clear focus and without visionary people in the team everything will stagnate soon or later. Engineers are often too busy to fix or to make small improvements to what they had instead of thinking what people want.
And that was just how things screwed in there. People were just too busy to destroy what Project Indiana was trying to do. "Desktop is not our focus. Servers are." But no one is going to run a server OS they don't know about.
People run Linux because they know it. They use it at their home and since it is good enough for servers, they started to use it there as well.
But how many people know illumos? They didn't advertise it. They just worked with small companies with enterprise focus and made tiny improvements.
Userland is rotting. They are still using the old plain sucky Sun userland, instead of modernizing it.
The kernel saw no improvements at all.
They are just doing what OpenBSD guys often do: pushing a normal commit to master and advertising it as an innovation.
Oracle released Solaris 11 with ZFS encryption. illumos had a PR opened but no one worked on it. For years.
Then when it was becoming clear that illumos was taking the path of the zombies, OpenZFS was born, in a tentative of separate it from the fate of the illumos-gate.
And now ZFS is mostly developed on Linux. OpenZFS reference implementation is not illumos-gate's implementation anymore. It is ZOL's (ZFS on Linux).
FreeBSD are rebasing their ZFS on ZOL. OpenZFS on Mac and Windows did the same.
And while illumos was stagnating, Linux integrated eBPF for DTrace-like capabilities, runs pretty well in the same workloads, has one of the best hypervisor and network virtualization capabilities out there, it integrated systemd for SMF-like capabilities (and it is way better than SMF) etc.
Many Sun engineers are working on Linux now. Adam Leventhal is working at Delphix, a company that joined illumos for their database solutions. Now Delphix is running Linux, leaving illumos on its own fate.
Joyent, the biggest contributor of illumos, was acquired by Samsung, and their Manta project died. Bryan Cantrill, its CTO and another ex-Sun, left the company.
Brendan Gregg, a famous DTrace expert and another ex-Sun and ex-Joyent, is now working on Linux performance at Netflix and he's one of the most known evangelist of eBPF.
The last nail in the coffin was the discontinuation of Unleashed, a fork of illumos that was trying to improve it by removing old crap and by replacing a lot of old and useless Sun userland with a FreeBSD-based one.
But the complaining of the community and their refusing to accept patches in the upstream was what caused the discontinuation of Unleashed.
Now its dev is working with FreeBSD, or at least that was what he said.
illumos died for lack of vision.
Its community was just a nostalgic group of people that still wanted to run Solaris, and yet they tried to tell people that illumos was not Solaris.
They didn't want to going forward, and the project payed the consequences.
If you want to run a Solaris 11-like environments, nowadays your best move is running some Linux enterprise distributions like RHEL or running FreeBSD.
illumos is no more.