What's a good (free) visual merge tool for Git? (on windows)

On Windows, a good 3-way diff/merge tool remains kdiff3 (WinMerge, for now, is still 2-way based, pending WinMerge3)

See "How do you merge in GIT on Windows?" and this config.

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Update 7 years later (Aug. 2018): Artur Kędzior mentions in the comments:

If you guys happen to use Visual Studio (Community Edition is free), try the tool that is shipped with it: vsDiffMerge.exe. It's really awesome and easy to use.

I've also used Meld. It's written in python. There is an official installer for Windows that works well.

Install it and then set it as your default mergetool.

$ git config --global merge.tool "meld"
$ git config --global mergetool.meld.path "C:\Program Files (x86)\Meld\Meld.exe"

If using a GUI GIT client, try the following (instructions for SourceTree, adjust accordingly)

• In SourceTree, go to Tools/Options/Diff
• In External Diff Tool, choose Custom
• Enter C:\Program Files (x86)\Meld\meld.exe in Diff Command and $LOCAL $REMOTE in Arguments
• In Merge Tool, choose Custom
• Enter C:\Program Files (x86)\Meld\meld.exe in Diff Command and $LOCAL $MERGED $REMOTE in Arguments

I've been using P4Merge, it's free and cross platform.