existing prototypes

I'm quoting from a presentation I gave on this topic:

• xText by the OpenArchitectureWare team
  
• TCS, by Frédéric Jouault (INRIA)
  
• TEF, by Markus Scheidgen (Uni Humboldt)
  
• Gymnast, by Chris J Daly (IBM)
  
• SAFARI (just about to become an Eclipse project)
  

Actually each of them has its unique approach towads jumpstarting a toolset for a custom DSL. Comparison would be a lengthy, lengthy, affair. I can sum it all up by saying that, provided your requirements fit the design criteria of your tool of choice, they'll save you a lot of work.

A hard test for any IDE generator for a custom DSL is whether the input specification encodes more constraints than just grammar (I'm talking about well-formedness rules such as declarations-before-usages and type-checking rules. Same observations go for other tools not on this list). More details on this criteria can be found in the aforementioned presentation.