Beyond Compare - Beyond Compare allows you to compare files and folders.
Watchtower - "Watchtower monitors your competition's websites and alerts you to important changes instantly."
WinMerge - WinMerge is an open source differencing and merging tool for Windows.
LaunchKit - Open Source - A popular suite of developer tools, now 100% open source.
Meld - What is Meld? Meld is a visual diff and merge tool targeted at developers.
Material Design for Bootstrap 4 - Powerful and free UI KIT for the newest Bootstrap 4 and Material Design