WinMerge vs Fork

You can quickly copy changed lines (or files in folder comparison) in both directions with keyboard shortcuts. You can edit the files as well, with syntax highlighting of some languages.

Can show what files has been changed in a folder, allows comparing files in tabs.

Can show differences within a line.

Winmerge is a free and open source tool.

Select two files and compare them. Alternatively, select one file, navigate elsewhere, select the other file to compare.
Also supports drag'n'drop of files / folders from Explorer.
History of past comparisons.

Binary is less than 3 MB, so it starts quickly

Can filter out files for folder comparison, lines for file comparisons, with regular expressions.
Options also allow to ignore whitespace differences, white lines, case change, line-ending changes, etc.

Keyboard shortcuts (and toolbar buttons) to navigate to next (previous) difference, side panel shows a map of the files with changed lines and allows to jump to a given place.

Detects when a block of lines has been moved in the file and shows the relation.

This feature is superior to the one that is implemented by SourceTree as it does not reset the file scroll view to the top of the file after each stage.

If you do feature-specific commits after some time of development - it's very important to be able to easily compose the commit from different line-based changes.

Several repos can be open at once in individual tabs, so it's trivial to switch back and forth between them.

The GUI components are flawless on the Mac. It is expected to be a similar experience on Windows. Once you realize that you can filter by branch, your appreciation for the product will go up dramatically.

This is an update from previous versions.