Most of my friends would take violent exception if I didn't talk a little about the Eclipse phenomenon. IBM used to have a Java IDE called VisualAge. According to polls, it was the second most popular Java IDEusually losing to Borland's JBuilder. When IBM decided that open source was a good thing, they discontinued their award-winning IDE and invested time and effort into the Eclipse projecta new open source platform and language-independent IDE.
Now in version 2.0, Eclipse forms the basis for a growing number of commercial offerings, including WebSphere Studio and Rational's XDE.