MacOSicons.com - Free 5000+ macOS app icons in the style of macOS Monterey, Big Sur. Fully open source and community led. How to install custom icons on macOS Monterey, Big Sur.
IconsExtract - Extract icons and cursors stored in EXE, DLL, OCX, CPL files
Moka Icon Set - Free Moka icons in various UI design styles for web and mobile. Download free static and animated Moka vector icons in PNG, SVG, GIF formats
IcoFX - IcoFX is an all-in-one solution for icon creation, extraction and editing.
Replacicon - Just updated to macOS Big Sur? You may have noticed some of the apps in your Dock look a bit inconsistent with the rest of the system.
IconViewer - Bot Productions's IconViewer utility allows you to view, copy, and save the icons in a file through its property sheet.