1. Aptana Studio 3 by Appcelerator, Inc
Aptana Studio 3 is currently release under “GNU General Public License“.
2. Adobe Dreamweaver CS5.5 by Adobe Systems
3. Eclipse by Eclipse Foundation
Open source community, whose projects are focused on building an open development platform comprised of extensible frameworks, tools and runtimes for building, deploying and managing software across the lifecycle. Platform independent as the IDE runs on Java JRE. Download the Eclipse PDT package for PHP support. Currently release under “Eclipse Public License (EPL)“.
4. Zend Studio 8 by Zend Technologies Ltd