TwoMillion is an easy rated Linux box that was made to celebrate 2 million users on hackthebox. The box includes API enumeration and abuse, along with a vulnerability for the Linux kernel’s OverlayFS subsystem that allows an unprivileged user to escalate their privileges to root.
The WriteFreely server was relatively easy to set up and only took 2 hours until it was fully functional. I decided on WriteFreely because I wanted something very simple, lightweight, and that also supported markdown for posting write-ups for Hack the Box content.