Question: What system do you recommend for implementing "automatic updates" for some java (desktop) application? I'd also want to have module/plugin installation and update. Think Eclipse and Firefox.

I'm aware of Eclipse RCP's OSGi stuff, and also NetBeans RCP has something here. Do one have to buy wholly into their respective RCP stuff to use their module and automatic update systems?

Are there other options?

Answer: 
Have you looked at the [Java Web Start](http://docs.oracle.com/javase/1.5.0/docs/guide/javaws/developersguide/faq.html)? It checks for updated module on the server and downloads it only if required otherwise things are cached locally on the client PC and starts from there.
I believe install4J now offers this functionality as part of their install builder (<http://www.ej-technologies.com/products/install4j/overview.html>) We've been wanting to check it out but haven't had a chance yet.