Scintilla is a free source code editing component. It comes with complete source code and a license that permits use in any free project or commercial product.

jEdit is a mature programmer's text editor.
# Written in Java, so it runs on Mac OS X, OS/2, Unix, VMS and Windows.
# Built-in macro language; extensible plugin architecture. Dozens of macros and plugins available.
# Plugins can be downloaded and installed from within jEdit using the "plugin manager" feature.
# Auto indent, and syntax highlighting for more than 130 languages.
# Supports a large number of character encodings including UTF8 and Unicode.
# Folding for selectively hiding regions of text.
# Word wrap.
# Highly configurable and customizable.
# Every other feature, both basic and advanced, you would expect to find in a text editor.

Vim is an advanced text editor that seeks to provide the power of the de-facto Unix editor 'Vi', with a more complete feature set.

Jext is a powerful and free source code editor written in Java, available for many platforms.

WinVi is a free editor for MS Windows.

• compatibility with Windows Notepad was my main goal
• nevertheless, it ought to be highly compatible with Vi
• a hexadecimal edit mode is available for editing binary files
• speedy program start because it is avoiding use of DLLs, MFC, etc.
• extremely large files editable with nearly no limitation by virtual memory
  (There is, however, a theoretical limit at 2 GByte)
• freely selectable background bitmap
• any font (variable spacing, TrueType, etc.)
• simple and clear handling with the availability of a toolbar and a status line
• support for Unix text file format
• fast change of character mappings for DOS files
• automatic word completion in command line (tab key)
• print support with choosable font (double column available)
• multiple language support (English, French, Spanish, or German)
• support of mouse wheels

Syn is an Open Source Text and Programming Editor with Syntaxhighlight for many Languages, and some IDE Features, like starting a program (e.g. Compiler) and capture the output, support for Projects etc. Syn is written in Delphi (Version 5, Updatepack 1) for maximum performance, stability and filesize ;-), hence it doesn't require any bulky VC++/VB Runtime or MFC libraries!

Notepad++ is a free source code editor (and Notepad replacement), which supports several programming languages, running under the MS Windows environment.
This project, based on the Scintilla edit component (a very powerful editor component), written in C++ with pure win32 api and STL (that ensures the higher execution speed and smaller size of the program), is under the GPL Licence.

SynEdit is an advanced multi-line edit control, for Borland Delphi and Kylix (C++Builder mostly works, but is unsupported).
It supports syntax highlighting and word-wrap, and it includes code completion and templates components, and exporters for html, tex and rtf.
It is a pure-VCL/CLX control, meaning it is not a wrapper for Microsoft Windows controls and so no run-time library is required.

Cream :: a modern configuration of the Vim text editor.

SETEdit a friendly text editor for DOS, Win32, Linux and other UNIXes