The Awesome Icon library is a free, high-quality icon library which defines in version 6.1.1 more than 2,000 free icons. It can be included in all kind of packages, and it does not depend on a CSS toolkit. It defines an icon font and SVG icons as well. The https://fontawesome.com website lists in addition to the Free version also a "Pro" and a "Pro Max" including more than 13K icons.
The package supports installation from CDN and a local installation, switchable via the site-wide administration link for the package in /acs-admin/package/fa-icons/.
The package is also already integrated with the <adp:icon> markup to support generic pages using icon sets depending on the "IconSet" definition (switchable per subsite).