Aaron,
I haven't looked at CodePlex, but there are three DSL-related workspaces on GotDotNet that I am aware of.
Software Factory Technologies in Microsoft Products (DSL, GAT, etc.): http://forums.microsoft.com/MSDN/ShowPost.aspx?PostID=798653&SiteID=1
Some discussion; doesn't appear to contain any code.
VSTS Work Item Type Designer: http://www.gotdotnet.com/workspaces/workspace.aspx?id=d03b00f5-7c5d-4e29-86b5-b966a04e1ed7
A designer to build Work Item Types for Team System. The code is from a pre-June version of the CTP, and the workspace owner, DarrenJ, is currently finishing writing a book on BizTalk 2006 for Wrox, so I don't think he will be updating it in the near future, although another member of the workspace might.
DSL Workshop: http://www.gotdotnet.com/Workspaces/Workspace.aspx?id=dae43a90-7893-493c-804a-e1f7537732c0
Contains three projects:
(1) an example "HowTo" project demonstrating various techniques - not a coherent designer as such.
(2) an "ExtensibleDSL" project - experiments in creating a target designer that can be extended post-deployment through configuration and additional UI and rules assemblies.
(3) an implementation of a standalone text templating host.
Again, all three projects need to be migrated to the release version of the DSL Tools. The workspace owner (me!) assures me this will be done when he gets a chance.
In addition, Edward Bakker has a blog describing a designer he is building: http://www.edwardbakker.nl/.
I'd also be interested in knowing what other projects are out there that people are working on.
Duncan
Might-be-interesting parts:
Gokhan
ActiveWriter is an interesting example. Thanks for posting the link!
Also interesting are all the Micosoft copyrighted source files that go into a DSL project. On one hand, I can see that this can make community projects a tad more difficult to get going, but on the other hand, the DSL Toolkit is a beautiful piece of work and their work deserves protection.