https://en.wikipedia.org/wiki/Eggdrop
https://www.tclarchive.org (Blast from the past!)
I was surprised to see that it is still under development.
After Eggdrop, it was Supybot that got really popular, although it is written in Python.
I still maintain a bot that began life as a mirc script, then a long time as an eggdrop bot, then ported to python based slackbot, and now most recently a python based discord bot.
Over the last 25 years it really has been a huge part of the way my group of friends interact. I recall the sheer wonder that I experienced when I learned about eggdrop bots and the huge amount that I learned while flailing around with tcl.
Same! It is quite interesting, I have not heard of it before.
My first experience with Tcl was through Eggdrop. I was really young at the time! I remember those mIRC scripts and different mIRC clients or something, they may have been through plugins? I don't recall, but I remember after installing them my mIRC looked very different and so on.
After Eggdrop came Supybot which was really popular at the time, then after that I just made my own. I have a Discord bot as well, I made it myself, although it is written in Lua because I made it around the time I was tinkering around with the language.
A more recent experience with Tcl was modifying Tclsh to make it suitable to be used as a replacement for bash. It works quite well now, I would say. Actually, a friend of mine did most of the job but still!