VSD/VSS is an MS Visio binary file format. While many people think that
Visio is a 'business graphics/diagram' creation program, it is a powerfull
application with advanced ability to support complex solutions extandable
by add-ons and through programming interfaces. It's not surprise, that MS Visio
works only under win32. There are no MacOS X or Linux versions.
In the diagram creation part it can be mostly substituted by Free Software
like GNOME Dia, KOffice Kivio or OpenOffice.Draw. GNOME Dia also has some
add-ons for database and software developers, UML supporting tools etc.
The main issues for those analogues are lack of interoperability with Visio
and near the absence of technical clip-arts ('stencils' in Visio terminology).
To interoperate with Visio an application has to be able to open files in Visio
own formats. Before introduction of XML-like office document formats in MS Office 2003,
Visio has been using VSD for documents and VSS for stencils. Since Visio 2k3 it's a non-default
option to save documents in VDX and stencils in VSX formats.
For years it was considered very hard to make an importer for those formats.
There is a tool for VSD/VSS file format research. You can take it here.