I desire to install this Addon: https://mahsu.com/hair-tool-v2-0-14-for-blender-2-8-free-download-full-version/ . My OS is Ubuntu 18.04
I am accustomed to installing Addons as .zip files. But this is delivered as a .rar file. The Addon browser sees the .rar file when I disable the filter. I did install it. But when I attempt to enable it I get the error “ModuleNotFound: No module named ‘Hair Tool v2’” error.
How is this Addon installed?
I haven’t tried it, but downloaded it. The rar is a zip file type, I used 7 zip [free] to open it to find it has a init.py that will load the addon.
In blender, go…preferences…“install…” at top bar…navigate to your unzipped folder… I usually pick the init py…this didn’t work. Tried pick the auto_load.py and no work. Restarted blender and can’t find the addon listed anywhere. I have all types selected, ie… Official, Community, Testing.
using blender 2.83.1 tried the last 2.82a march… no luck
Will try more later and get back to you. If you discover the way post it here.
I am on a windows laptop, my Linux box was hit with ‘Melt Down Attack’, trying to fix it.
Well, you are using the wrong download link for starters. Hair Tool can be found here: https://gumroad.com/l/hairtool
Besides - that is a pretty outdated version, according to the version history it won’t work with current releases. But I think @JoseConseco might be able to tell you more about it. 
I give not support for copies of my addons distributed on some reandom sites
I didn’t expect you to. 
I thought you might want to know about people warez-ing your addon.