Java Web Start is an application-deployment technology approved by Sun Microsystems for the deployment of Java apps.

The goal of JWS is to provide a mechanism for distributing an application to a user base in such a way that it does not have to be installed on any machine, keeping the entire application on a web server.

Keeping the entire application in one place makes upgrading it very easy. Once upgrades have been completed you replace the old version on the server with the new one and instantly all of your users are using the new version. There is no regression issue.

As is true with everything, Web Start has downsides.

All of your user-base has to download a Web Start client application. The client is easy to set up, but it adds a step in the process. It also somewhat alientates any users who are connecting to the internet over a modem.

As a solution for a company, which is trying to distribute an application to its employees, who all have broadband connections to the internet at their desks, Web Start could be a perfect solution. In the future, as broadband propogates and becomes more common we could begin to see commercial applications using this type of technology, so that we won't actually have applications installed on our computers, we will just connect to the application over the internet in order to use it.

More can be found at http://java.sun.com/products/javawebstart/