Wikipedia
JUpdater
JUpdater is a project which aims to create a utility that allows developers to quickly implement version checks into Java programs. The utility ensures that the user can always be notified of new versions, and easily upgrade to the latest version from within the program, without having to do anything. The utility only downloads the files that are out of date, saving bandwidth.
JUpdater is split into two parts. A small Java client, which can easily be implemented into existing programs, and a PHP server part, which keeps track of the versions and provides the client with all the info it requires. The project is still in development, possibly containing bugs. Any program that is to be updated via JUpdater has to be contained in a jar file.