This script displays the chord name of MIDI notes in a nice little box inside your MIDI Editor at the top left corner like this 👇

This script was made by FeedTheCat, to learn more and support him please check out his forum thread!
You just run the script once and a little box in your MIDI editor will appear detecting chords. It works via either hover, select notes or even live MIDI input.
Not only that but it can also drop markers or regions in your project with the chord names! Just right click on it and it will give you a bunch of options. Including a setting to auto-run this script so it always works!
I had no idea it was possible to embed scripts inside the UI but this was a nice surprise~
How to install
1. Import the lil chord script:
Copy and paste this link into: Extensions > ReaPack > Import a repository
https://raw.githubusercontent.com/iliaspoulakis/Reaper-Tools/master/index.xml
2. Import js_ReaScriptAPI extension:
This is an extension that can be installed via Reapack.
Copy and paste this link into: Extensions > ReaPack > Import a repository
https://raw.githubusercontent.com/ReaTeam/Extensions/master/index.xml
3. Running the script
You should now have the following script in your Actions menu at the MIDI Editor section:

Just run it once and then you can see it working in your MIDI editor.
If you want the script to always be there, just right click on it and select Run script on startup.
