This is a very small and simple app. Just install the app and all external URLs and attachments in the attachment overviews will open in a new browser tab.
Clicking on a link leading to an external pages will open the page in a new tab, while clicking on links leading to pages inside Confluence opens them inside Confluence.
Optionally you can define a CSS class, which will be added to every external URL and attachment link element (in attachment overviews only) in Confluence. This allows you to configure a different display style for external links in the Confluence Stylesheet.
You can find External Links configuration at
> Manage Apps > External Links for Confluence > Configure