WinMerge is an Open Source (GPL) visual text file differencing and merging tool for Windows. It is highly useful for determing what has changed between project versions, and then merging changes between versions.
See the screenshots page for more screenshots.
WinMerge 2.8.6 – latest stable version
WinMerge 2.8.6 is the latest stable version, and is recommended for most users.
Para comparar EXCEL, hay que instalar antes este plugin
With this plugin you can compare Word, Excel, PowerPoint, PDF and some more files.
For more details and the download go to the xdocdiff plugin homepage.