See the DSL Tools web page for details on the latest preview of the DSL Tools.  Here's what the link says:

About the Latest CTP
The latest CTP (in the June CTP of Visual Studio 2005 SDK) brings the Domain-Specific Language tools much closer to their final form for the release of the first version. The APIs, code generators and new Domain-Specific Language definition format are close to their final form. However, the designer for editing Domain-Specific Language definitions, which replaces the Domain Model Designer, has missing features and bugs. So, if you are prepared to edit a Domain-Specific Language definition directly in XML or using the Domain-Specific Language definition designer, but being careful to take account of the documented known issues http://msdn.microsoft.com/vstudio/dsltools/knownissues/default.aspx, then this CTP will give you access to all the improvements and new features detailed below. Otherwise you may continue to use an earlier CTP of DSL Tools, such as the CTP included in the April release of the Visual Studio SDK, and rely upon a more stable and documented authoring experience.

New features of this release include:

  • Simplified and cleaner APIs.
  • A new Domain-Specific Language definition (.dsl) format which replaces the .dsldd and .dsldmd formats. As a result of this change, you can define more behaviors and customize the properties grid and the model explorer without writing custom code. The new format also supports a richer, more flexible and less constraining mapping between notation and domain model aspects. In addition the format provides numerous flags that indicate places where custom coded behavior is required.
  • A preview of the new Domain-Specific Language designer, which you can use to edit domain-specific language definitions. Some features in the designer have not yet been implemented. For more information, see the known issues document http://msdn.microsoft.com/vstudio/dsltools/knownissues/default.aspx.
  • A new set of code generators. Among other improvements, these generators produce code that is easier to customize by hand.
  • A new Domain-Specific Language Designer project template, which has an improved wizard UI and which produces a solution that has an improved project structure.
  • Support for ports notation.
  • Support for swimlane notation.
  • A new approach to the serialization of models in XML, where:
    • The XML format used is more readable, with tags that match the domain concepts.
    • You can make simple customizations to the XML format in a Domain-Specific Language definition, and you can plug custom code into the generated serialization code to handle more complex customizations.
    • The XML reader tolerates elements that are missing or that the reader does not understand, and the error checking is considerably improved.
    • Model and diagram information are saved in separate files, so that you can build designers for viewing existing XML formats.
  • Various performance improvements, in particular to model loading and the text template transformation engine.
  • Updated and extended documentation, including more documentation of the APIs and new walkthroughs to match the new experience.