These plugins are written in Jesusonic (jsfx file extension). The files are simply text files that Reaer compiles on the fly. So you can open them with a word processor and read the source code. Sometimes further installation/usage instructions are there too. Running jsfx files requires either Reaper or ReaJS. To install:

Download Reaper or ReaJS, the latter lets you run these apps inside your own DAW (windows only).

If using Reaper:
In Reaper, choose Options/Show Reaper Resource Path, and move the plug-in to the Effects/MIDI subfolder.
Quit Reaper and re-launch it, so it re-scans and can find this file.
Make a new track, control-T.
Put this effect in the track's FX rack (click the square FX button, type the plugin's name in the filter box, then double-click it)

If using ReaJS:
Install ReaPlugs as you would any other VST.
Go to the directory you installed it in and look for the ReaJS folder. Look for the other JSFX files.
Move this file to the MIDI directory.
Run your DAW, load ReaJS as you would any other VST, and load the file into ReaJS.

EarTrainer41 is an ear trainer for 41edo, as well as a notation guide and an ambient music generator!

NoteNamer names every note in every edo in ups and downs notation. Please borrow from this well-commented code to add ups and downs to your microtonal app!

StarMaker displays rank-2 scales in a circular format.

PergenLister categorically lists every single rank-2 temperament imaginable.

EDO-strobetuner is a strobe tuner for microtonal instruments. Extremely accurate.

Web apps from others