Gedit has tabs, multilanguage spellchecking and automatic file backup. There's full undo and redo, as well as search and replace.
In it you'll find many usefull features for coding, such as bracket matching, text wrapping, current line highlighting and line numbering.
There's syntax highlighting for many languages, for example C, C++, CSS, HTML, Java, Perl, PHP, Python.
It also has support for remote file edits via GNOME VFS libraries, and it's possible to dynamically add new features such as snippets and integration with external applications.
Gedit has a plugin system, with plugins for things like
- LaTeX integration
- collaborative writing
It's UTF-8 compatible and has free licensce.