Andrew Cunningham at Ars:
Apple put the final nail in the Xserve’s coffin in January 2011 when it officially stopped selling rack-mounted servers. Instead, the company started pushing server customers toward Mac Pros and Minis. On Sept. 20 of this year, Apple lowered that coffin into the ground when macOS Sierra dropped software support for the systems. And while Xserves running El Capitan will keep getting security updates for a couple of years and the current build of the macOS Server software still runs on El Capitan, the hardware will soon be completely buried.
For a few years after the Xserve’s death, the company offered Mac Pro and Mac Mini Server configurations (PDF) that could do some of the same things, but even those options eventually disappeared. Even though Apple never offered true server-class hardware again, that doesn’t mean the hardware isn’t still out there doing its job.
I actually know of several people who still run Xserves to this day. They were hardy rack servers that did their job loudly.