Download and unzip

Get the zip, unpack it into a normal folder, and learn why there is no installer.

MeshOptimiser comes as one zip file. There is no installer. Everything, including its Python environment, lives in the folder you unpack.

Open the Download page of this site and press the download button. Your browser saves a zip file, usually in your Downloads folder.
Unpack the zip. On Windows, right-click it and choose the option to extract everything. On macOS, double-click it.
You now have a folder, named something like MeshOptimiser-main. Move it wherever you like, for example into your Documents folder.
Open the folder. You should see files called start.bat, start.command, serve.py and index.html, among others.

Where to put the folder

Somewhere you are allowed to write files. The app creates two folders inside its own: .venv for its Python environment and inbox for converted files.
On a drive with about 2 GB free.

To remove the app later, delete the folder. Nothing is installed anywhere else, apart from Python itself if you installed it for this.