Open Source Windows Version Control Software

TortoiseSVN is a Subversion (SVN) client, implemented as a windows shell extension. Which means it's available right where you need it: in the Windows file explorer. It's intuitive and easy to use, since it doesn't require the Subversion command line client to run. Simply the coolest Interface to (Sub)Version Control!

WinMerge is a Windows tool for visual difference display and merging, for both files and directories. It is highly useful for determining what has changed between file versions, and then merging those changes. WinMerge has Unicode support, Flexible syntax coloring editor, Visual SourceSafe integration, and Windows Shell integration. Regexp filtering for filenames and lines. Side-by-side line difference and highlights differences inside lines. A file map shows the overall file differences in a location pane. The user interface is translated into several languages.

TortoiseCVS is an extension for Microsoft Windows Explorer that makes using CVS fun and easy. Features include: coloured icons, tight integration with SSH, and context-menu interactivity.

A simple easy-to-use application for "visually editing" large patch files (unified diff files); different patches/diffs/folders/files can be selected/deselected, the resulting patch file can be saved and/or run against a source tree (e.g.).