Beyond Compare - Beyond Compare allows you to compare files and folders.
dupeGuru - dupeGuru is a tool for finding duplicate files on your computer.
WinMerge - WinMerge is an open source differencing and merging tool for Windows.
Czkawka - Multi functional app to find duplicates, empty folders, similar images etc.
Meld - What is Meld? Meld is a visual diff and merge tool targeted at developers.
AllDup - AllDup is a freeware tool for searching and removing file duplicates on your Windows computer.