LiteIcon - LiteIcon is a simple app which allows you to change your system icons quickly and easily.
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.
JDraw - Open Source SF.net
IconsExtract - Extract icons and cursors stored in EXE, DLL, OCX, CPL files
WinIcon Customizer - WinIcon Customizer is the standard way to change all the icons on your Windows PC.