Eclipse
Eclipse is another free Java IDE for developers and programmers and it is mostly written in Java. Eclipse lets you create various cross platform Java applications for use on mobile, web, desktop and enterprise domains.
Its main features include a Windows Builder, integration with Maven, Mylyn, XML editor, Git client, CVS client, PyDev, and it contains a base workspace with an extensible plug-in system for customizing the IDE to suit your needs. Through plugins you can develop applications in other programming languages some of which include C, C++, JavaScript,, Perl, PHP, Prolog, Python, R, Ruby (including Ruby on Rails framework), to name just a few.
Eclipse is available under the Eclipse Public License and is available on Windows, Mac OS X and Linux.
Eclipse IDE for Java Developers