http://geany.org
Geany is a GPL
TextEditor / lightweight IDE for UNIX/Linux using GTK. A Windows installer is also available that bundles the required GTK libraries.
It has the only implementation I've seen of something very useful, a checkbox to invert the colors to give a quick white-text-on-black editor.
Here's it's feature list from Wikipedia:
- Auto-completion
- Multiple document support
- Project support
- Syntax highlighting
- Code folding (partially)
- Symbol lists
- Code navigation
- Embedded terminal emulator
- Customizable build system to check, format, compile and execute code
- Send selection to external tools
- Extensible via plugins
It has plugins for
VersionControl integration (*nix only), scripting with
LuaLanguage, online documentation browsing and window splitting.