Till now, this IDE was available only on Windows and Solaris. You can download NetBeans for free, just as you could when it was part of an independent company. What's changed is that Sun brings a lot more publicity. Perhaps Borland acted in response to Sun's purchase of NetBeans. Or perhaps the low-end Java IDE market just isn't what it used to be.
Some more reasons appear here .
In any case, you can now download JBuilder 3 Foundation for free. The Foundation part of the product name means that this is the base product. Right now, only the Foundation version is available on Linux.