Most Java developers realise that it is inefficient to instantiate a separate JVM for each Java application running on a user's computer. This involves a significant extra start-up time and is wasteful of memory. Unfortunately, due to the need to segregate the effects of one application from another there hasn't been any choice.
On the server side however, much progress has been made in the area of Java Application Servers which are able to run multiple web applications within the same JVM.
The idea behind this project is simple: take the compartmentalisation technology which has been developed for servlets and reapply it to the desktop space.