I then saw nice instructions by /u/Reichstein on /r/ChromeOS to install a different program on Chromebooks, but I used his wording and rephrased it to Mudlet. So here it goes:
I hope this helps!If you are on beta channel your device should have updated to 69 (or will soon).
Once you are on version 69, have a look in settings, just under "google play store" you should see "Linux (Beta)".
Click that and follow the instructions to install the linux VM (pretty much just clicking next a few times).
Once that's done you should have a "Terminal" app in your app list.
Open terminal and use the command "sudo apt-get install mudlet" to download an install Mudlet.
I should mention that not all devices support linux apps, so if you are on 69 but don't see the "Linux (Beta)" option your device may be unsupported at this time.