Microsoft Plans Visual Studio Shell

Visual Studio Shell, a scaled-down version of Visual Studio, it is intended to allow developers to build Visual Studio functionality atop their own vertical tools, as well as integrating various languages such as Fortran, Cobol, Ruby and PHP.

Developers will be able to use Visual Studio Shell in two modes: integrated and isolated. The integrated mode is built upon Microsoft's existing Visual Studio Premier Partner Edition 2005, primarily used by language integrators.

The isolated option allows partners and developers to build products on top of Visual Studio, with the ability to customize the experience so that it doesn't necessarily look like Visual Studio
for more information visit Visual Studio Extensibility , and Craig Skibo's WebLog