The Mac User group has been looking for an economical replacement for a 2007 XServe (originally donated by Apple in 2009) to run the OpenText FirstClass BBS they use. The latest FC Server software needs better than OS 10.7.5, which is the best that model of XServe can deliver.
Finally the Treasurer decided she & her husband could part with their 2012 Mac Mini for a fair price. This is a 2.3 GHz Core i7 quad-core machine currently with 4 GB of RAM. It'll cost an extra $160 to upgrade the RAM to 16 GB & $600 to the Mac itself, $31 for macOS server & about $150 more for a suitable rackmount.
An Apple reseller quoted $2100 to upgrade a 2014 2.8 GHz Core i5 dual-core Mac Mini to 3.0 GHz Core i7 & 16 GB of RAM. This is without the rackmount.
You'd think the 2.3 GHz i7 wouldn't be as good a processor as the 3.0 GHz i7 but the telling factor is the former is a quad-core vs the current model's dual-core. Under Geekbench testing, the older 2.3 benchmarks at more than 25% faster than the newer one.
So under $1000 vs over $2000, no contest. The older & better machine will be come into service very soon.