This tool opens a file or URL with the default application associated with it on the user's operating system:

• On macOS, it's equivalent to the open command
• On Windows, it's equivalent to start
• On Linux, it uses something like xdg-open, gio open, gnome-open, kde-open, wslview as appropriate

For example, it can open a web browser with a URL, open a PDF file with the default PDF viewer, etc.