This is a Visual Studio add-in that automates the AssemblyVersion control. That's useful for managing version of multiple assemblies.
From the introduction:
As suggested on George Shepherd's Windows Forms FAQ, a simple solution to synchronize versions among multiple projects is to extract version information into a single file and reference it from each project. However, that approach has one drawback: if an assembly is used in different solutions, you may end up having two different versions of actually the same assembly.
The purpose of this add-in is to help the user to manage and synchronize all these versions, especially for solutions that contain several projects. There is already a solution provided by Darriel Liu (Build Number Automation for Visual Studio .NET Projects) where he created a Visual Basic macro that modifies the AssemblyVersion, basically following the original approach by Microsoft. This solution is written in C#, and extends the original idea, providing GUI for more control, and enabling managing all three version types either independently or synchronized. It also provides a mean of automatism to simplify versioning as much as possible.