The Wisext tools run on the 3D modelling desktop software SketchUp developed by Trimble Inc.
You can download and install the desktop version of SketchUp from the official sketchup.com site: https://www.sketchup.com/fr/download/all
SketchUp Make 2017 is the last desktop version that you can use for free (for non-commercial use) and that supports the extensions. Sketchup Make 2017 is unfortunately no longer available on the official Sketchup site. Some sites offer to download the 2017 version (for example: cnet.com ). You must remain very careful and pass the downloads to the antivirus.
From the 2018 version, there is no more desktop free version and you must pay a license. Since 2020 there is no more perpetual license and you must pay an annual subscription.
The online SketchUp versions do not support the extensions. It is impossible to use the Wisext tools on the version for web (SketchUp Free, SketchUp Shop).