jEdit
This is just a short note. I couldn’t go much further without recommending my key tool without which I could not live. That is jEdit with a variety of plugins. By itself, jEdit is an excellent little text editor. With plugins it can provide a wonderful development environment. I tried test versions of a number of editors before ending up with jEdit, and I think there is no question this one is king of the free editors.
If you need one of these for development, you probably know enough to work through it, so I’m not going to go into any “how-to” details–just make my recommendation.