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)
External Diff Tool
, choose CustomC:\Program Files (x86)\Meld\meld.exe
in Diff Command and $LOCAL $REMOTE
in ArgumentsMerge Tool
, choose CustomC:\Program Files (x86)\Meld\meld.exe
in Diff Command and $LOCAL $MERGED $REMOTE
in Arguments