WinDiff
From Wiki @ Karl Jones dot com
WinDiff is a graphical diff utility program published by Microsoft (from 1992).
Description
WinDiff is distributed with Microsoft Windows support tools, certain versions of Microsoft Visual Studio and as source-code with the Platform SDK code samples.
WinDiff was included in the Windows SDK (previously known as the Platform SDK, previously known as the Resource Kit) until Microsoft Windows SDK for Windows 7 and .NET Framework 4 (a.k.a. Windows SDK 7.1).
Because portions of the Windows SDK were shipped in Visual Studio, WinDiff was also included in Visual Studio until Visual Studio 2010.
WinDiff was removed from the Windows 8 SDK and therefore is not included in Visual Studio 2012 or any later version.