At PDC this week, Microsoft has presented the OSLO tool suite. It is their new modeling initiative. They have a language infrastructure called M for building textual languages, specifically, they have the Mg language for defining grammars. They also have tool called Quadrant for building graphical DSLs. Finally, they have repository for storing the models, for access at build time and runtime. AFAIK, their ability to customize editors is limited, at least I haven't seen anything about it (Martin Fowler, says they have something...).
So this is certainly an interesting technology to follow! Here are some pointers:
Martin Fowler has a nice writeup
that provides a good overview. The sessions at PDC
will be available as video soon, I am told. TL27 and TL31 seem interesting. Finally, there's a set of docs, and also a download package available here
If you're playing with it, I'd be interested in your expieriences....