(Copy/paste from the GEF FAQ) Can I develop a standalone GEF application without use of the Eclipse platform? The official answer is No, this is not supported. The main reason involves the use of an Eclipse-specific file titled plugin.properties which GEF uses for string externalizations. However, since GEF is an open source project, modifications to the GEF codebase could potentially allow a GEF editor external to Eclipse.
NEVER EVER try to modify an EMF model if someone else has modified it without updating from CVS first. When synchronized via CVS, tons of conflicts arise and many are hard to resolve. For example, the autogenerated code numbers all classes in a diagram. Therefore, the merger of both codes introduce duplicate ids which are hard to resolve.