Usually, all you have to do to install ReText, is:

1. Install Python 3.

2. Install pip for python3:

   $ sudo apt install python3-pip
   

3. Run this command:

   $ python3 -m pip install ReText --user
   

   The --user argument is needed for local installations, drop it and run the command as a superuser if you want to install ReText system-wide.

ReText should be available in your desktop’s menu (because it ships a .desktop file), but you can also simply run retext to launch it.

If ReText is available in your system repository, install it from there.

For example, on Debian or Ubuntu, run:

# apt install retext

Note that the version provided by the distro isn't necessarily the latest version provided here.

Note: these systems are in no way officially supported. Use ReText there at your own risk.

On Windows, pip will also install a retext.bat file to make it easier to run ReText.

There is also an unofficial portable app available for Windows.