Komodo Edit is an open source editor by ActiveState that is different from your run-of-the-mill editor in that it has many features that are usually absent in editors, but you might find in IDEs (integrated-development-environment). Actually Komodo Edit could easily be considered a lightweight IDE.|
The user interface is very organized, using four main areas and a menu and toolbar. Some editors have a few buttons in the toolbar that you need and a couple dozen more that you might use once in a lifetime - if you live for a couple of centuries! Komodo Edit has the buttons you need and very little else. Simplicity is always a good thing!
Komodo Edit lets you edit multiple documents simultaneously so it does have tabs, just like the best editor you can buy. You can also have Komodo open up the files from the last session which saves time.
One of the best features of Komodo Edit is its autocompletion capabilities. It supports Perl, PHP, XML, Python, Tcl and more. If you normally use an IDE, you'll find that Komodo Edit fills all your requirements and even more.
You can create a toolbox for the tools you're using in your current project and have them available in a toolbar or menu. That's just about the ultimate in convenience and very, very nice to be able to work with!