I run a few servers that I use for experimentation and learning. Currently,
my lab consists of an HP Z420, Dell Optiplex 780,
Raspberry Pi 2,
These systems are not traditionally found in a homelab, but they allow
me to experiment with many technologies at a low cost, both upfront
and in terms of power. The ARM systems (Raspberry Pi, ODROID-XU4, Rock64 and
RockPro64) are especially good for this.
All these systems run NixOS, an innovative Linux
distribution, with other OSes running in containers and VMs.
Some of the services and technologies currently in use in my lab are NixOS,
Docker, NGINX, ZFS, Flask, KVM/libvirt, InfluxDB, Telegraf, Buildbot, OpenVPN,
BIND9 (DNS server), Syncthing, and Sanoid.