Fully-featured Java IDE written completely in Java, with many modules available
Edit by : The NetBeans IDE is a free, open-source Integrated Development Environment for software developers. You get all the tools you need to Create professional desktop, enterprise, web and mobile applications, in Java, C/C++ and even Ruby. The IDE runs on many platforms including Windows, Linux, Mac OS X and Solaris; it is easy to install and use straight out of the Box.
Highlights
-Easy-To-Use Java Gui Builder

-Create professional-looking Java GUIs by placing and aligning components on a canvas.

-Visual Web and Java EE Development

-Build standards-based web applications visually using Ajax, CSS, and JSF. Full set of tools for EJB development.

-Visual Mobile Development

-Create, test and debug GUI applications that run on mobile phones, set-top boxes, and PDAs.
Visual UML Modeling

-Separate software design from implementation with UML Modeling.

-Ruby and Rails Support

-Powerful Ruby editor (with code completion), debugger, and full support for Rails. Includes the jRuby runtime.

-C and C++ Development

-Full-featured C/C++ editor, debugger, project templates, and support for multiple project configurations you can free download NetBeans IDE for Solaris(sparc) 6.1 now.