Things like ZFS, Zones, DTrace, SMF, and Crossbow were locked up inside Sun Solaris for many years because it was proprietary. The effort to open source it took a long time and because of how Solaris was built (with various third party things) Sun essentially had to release under a slightly odd license, the CDDL.
Meanwhile Linux, which had ascended to dominance post dot com bubble, solidified its lead as the defacto default server operating system, a fairly well earned dominance built on being the first truly free Unix available for x86/PC hardware, and at a time when that was a truly lesser tier of hardware (unlike today).
But today I worry we've settled into a mindset of "the linux way is best because it is dominant" - if you use linux you can google your stack traces, you know that even if the tech is inferior (coughbtrfscoughsystemtapcoughsystemdcoughepoll*cough) many other people are in the same boat and in theory hordes of developers will -- might? -- make patches to fix the problem. No one ever got fired for choosing linux, basically.
I've migrated a bunch of personal projects to a server I own running SmartOS, an Illumos derivative. One thing I've learned is that it's actually really viable and nice these days to use an alternative operating system. I imagine it's similar with FreeBSD, OpenBSD, vanilla Illumos, etc. These systems run on a pretty impressive array of hardware and are able to leverage the near total standardization of the hardware/bios stack and the inroads made by other projects to bootstrap to viability. E.g. SmartOS uses pkgsrc from the netbsd project for packaging, took some boot technology from FreeBSD, and in general is able to tap into the universe of "unix like" tools, even if many of those tools are most often used on linux.
Anyway if you get a chance give this stuff a spin, it's pretty eye opening what you can accomplish. Zones, to me in particular, feel like a game changer.