Xtext is a framework/tool for development of external textual DSLs. Just describe your very own DSL using Xtext's simple EBNF grammar language and the generator will create a parser, an AST-meta model (implemented in EMF) as well as a full-featured Eclipse Text Editor from that.
The Framework integrates with technology from Eclipse Modeling such as EMF, GMF, M2T and parts of EMFT. Development with Xtext is optimized for short turn-arounds, so that adding new features to an existing DSL can be done in seconds. Still with the new version more sophisticated programming languages can be implemented.
Go to the project's website