
www.jedit.org
jEdit is a great text editor for programmers.
- It is free and opensource
- It is java-based (crossplatform)
- It's fast
- Very flexible
Plugins
Support of plugins is a key feature of jEdit

You can install/uninstall/update plugins with it. While installing you can read short description of plugin.
Project Viewer
Very useful plugin to manage project

You can have a lot of projects. And it is very useful to group them.
Docker
Dockes plugin window to jEdit

Commonly it's not very useful to have many windows. So this plugin makes it possible to dock window of plugins. For example, Project Viewer:
Sidekick
Displays structure of your source file

The SideKick plugin provides a framework for high-level language-specific features.
Currently, this includes a structure tree dockable window, commands for moving the caret and folding based on language tokens, and a basic code-completion framework.
The SideKick plugin does nothing by itself; at least one plugin providing a language parser, such as the XML plugin, must be installed. Currently available parsers for: Java, PHP, Ruby, Python, Perl, C/C++, JavaScript, XML, Fortran...
OpenIt
Quick access to file of project

OpenIt is my favorite plugin. It gives you an oppotunity to instantly open any file of your project by typing first chars of name. It's extrimly fast and very useful.
Has support of special symbols "*" and "?". So you can type "*controller.rb" to get all controllers of your rails project.