ISOLDE is designed as a plugin to UCSF ChimeraX, and should be installed via their internal package management framework. To obtain it, follow the instructions below.

1. Go to https://www.rbvi.ucsf.edu/chimerax/download.html#release and download the 1.6 release for your operating system.
2. Install and run ChimeraX
3. Go to Tools/More Tools... in the ChimeraX menu
4. Find the ISOLDE link in the browser window that opens
5. Click the big blue "Install" button on the right hand side, and wait for it to download/install. When complete, you will see a message in the ChimeraX log window.
6. ISOLDE should now appear in the menu under Tools/General/ISOLDE

If you encounter issues during installation, please first check to see if your problem is covered here. Otherwise, please contact me.