Wonder what they used to develop the IBM's Websphere Studio of products? One thing is for sure. These products are based on EMF models.
EMF is the short for Eclipse Modeling Framework. It helps in developing models and then generating code for it. The model is described using yet another model called Ecore (which is again based on EMF). This model is platform independent. Yet another model called the Genmodel holds platform specific information that is used to generate code. The code generation can be controlled using something called Java Emitter Templates (JET for short).
The Ecore model can be developed using XML Schema, Rational Rose models, Annotated Java, Emfatic (from IBM) etc.
The beauty of EMF is it is free and can be used with Eclipse.
For those of you, who have read till here, but couldn't get a word of it, and still want to know more (because you feel it can help you someway and you feel my description was not good), refer to the standard EMF site.
Also this interview with Dave Steinberg is worth a read.
EclipseCon also has some resources for EMF.
(And ya, you can refer to this site here for various other resources on Eclipse)