Some Visual Studio add-ins add commands to the Visual Studio tab context menu. For example, Power Commands and ReSharper add the Close all command. VisualSVN adds several commands and even a submenu:

VisualSVN commands in Visual Studio 2010 tab context menu
Tabs Studio creates its own tab context menu that doesn’t include Visual Studio or other add-in commands. The new XMenu add-in extends Tabs Studio context menu with external commands. XMenu scans all commands from Visual Studio tab context menu and adds those not from the default Visual Studio command set to the Tabs Studio context menu:

VisualSVN commands in Tabs Studio tab context menu
By the way, you can customize Visual Studio tab context menu as other Visual Studio menus and toolbars. The tab context menu is in Other Context Menus and named Easy MDI Document Window:

Tab context menu customization in Visual Studio 2010

Tab context menu customization in Visual Studio 2008
For non-document tabs (like Start Page) the context menu name is Easy MDI Tool Window. If you manually add a new command to a Visual Studio tab context menu, XMenu will also add this command to the Tabs Studio tab context menu.
Note, in Visual Studio 2010 to add a command to the right-click menu of a document’s tab, first you’ll need to right-click on a Visual Studio document tab to work around a Visual Studio bug. (Otherwise the Easy MDI Document Window context menu doesn’t show up in the Customize dialog.) As Tabs Studio hides original Visual Studio tabs, you first need to temporarily disable Tabs Studio or float a document to open original document’s tab context menu.
Download link: XMenu v1.0.0.