Komodo IDE from ActiveState is a rich IDE for Perl, Python, PHP, Ruby, JavaScript, XML, HTML and Tcl. It offers many integrated tools (i.e. code completion, code debugger, regular expressions toolkit, etc).
ActiveState also introduced an open-source, free Komodo-based editor, called Komodo Edit, which is less functional but available at no cost.
The source code is available from Open Komodo and is distributed under the Mozilla Public License. The source code to build Komodo Edit is available here.
The page titled "IntegratedDevelopmentEnvironments" includes several reviews of Komodo. Here, in April 2007, is one of Komodo 4.