gitk is a graphical history viewer. Think of it like a powerful GUI shell over git log and git grep. This is the tool to use when you’re trying to find something that happened in the past, or visualize your project’s history. Gitk is easiest to invoke from the command-line.
git gui focuses on allowing users to make changes to their repository by making new commits, amending existing ones, creating branches, performing local merges, and fetching/pushing to remote repositories. … git gui is known to work on all popular UNIX systems, Mac OS X, and Windows (under both Cygwin and MSYS).
vimdiff – edit two, three or four versions of a file with Vim and show differences. Vimdiff starts Vim on two (or three or four) files. Each file gets its own window. The differences between the files are highlighted. This is a nice way to inspect changes and to move changes from one version to another version of the same file.
Kdiff3 is an open source file comparison tool supported on Windows, OSX, and various flavors of Unix/Linux. It provides a easy to understand GUI for comparing files, directories, and merging files.
xxdiff is a graphical browser for viewing the differences between two or three files, or between two directories, and can be used to produce a merged version.
Kompare is a graphical diff and merge tool targeting developers. It allows users to compare two different text files or two directories. It is part of KDE Applications and therefore primarily used on Linux and other Unix-like operating systems, as well as Windows.
Diffuse is a small and simple text merge tool written in Python. With Diffuse, you can easily merge, edit, and review changes to your code. Diffuse is free software.
Helix Visual Merge Tool (P4Merge) is a three-way merging and side-by-side file comparison tool. Use it to visualize your merges, obtain comprehensive file history, and compare a broad range of image files.
Beyond Compare is a data comparison utility. Aside from comparing files, the program is capable of doing side-by-side comparison of directories, FTP and SFTP directories, Dropbox directories, Amazon S3 directories, and archives. It is available for Windows, Mac OS, and Linux operating systems.