TortoiseGit is a visual git client for Windows, it has a built-in compare tool with a side by side view which is the best tool that I found so far, make it very easy to compare.
GitHub Desktop is a free git client for Windows and Mac.
Sourcetree is a free git client for Windows and Mac.
GitKraken is one of the best-known Git GUI tools for Windows, Linux, and Mac.
Engineer Tips 
I guess Git Extensions should be named, when listing free Git Clients on Windows.
https://gitextensions.github.io
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