Java software lets developers write one set of code for programs that can work on different types of computers that run of a variety of operating systems.
That makes it possible for a Web developer to write one computer program using one set of code that can run on Windows machines, Mac PCs and other types of computers.
In addition, Sun has a version of Java that works on portable electronic devices such as cell phones, which it is also making available for free.
Until now Sun has only made Java available to paying customers who buy rights to use it as well as technical support for the product.
Sun last year made its Solaris operating system available to the open-source community as an alternative to Linux, a widely used operating system that has long been available for free.