AdminESP was a plugin I wrote in early 2018 for a Garry's Mod server I was running at the time. I noticed some players were using cheating software that let them see through walls, but it was hard to verify that suspicion without the ability to see players through walls myself. Thus, AdminESP was born.
After some use on my server, I opened up the source code and provided a complete package to install on other servers. However, my server was on the way out at that point, and sadly doesn't exist any more. Unfortunately, there's no way to audit how many servers have this code installed, so I can only hope other admins are using AdminESP to catch cheaters to this day.