TEA is a powerful and easy-to-use Qt4-based editor with many useful features for HTML, Docbook, and LaTeX editing. It features a small footprint, a tabbed layout engine, support for multiple encodings, code snippets, templates, customizable hotkeys, an "open at cursor" function for HTML files and images, miscellaneous HTML tools, preview in external browser, string manipulation functions, Morse-code tools, bookmarks, syntax highlighting, and more.
LyX is a document processor that encourages an approach to writing based on the structure of your documents, not their appearance. It is intended for people people who write and want their writing to look great without tinkering with formatting details, font attributes, or page boundaries. On screen, it looks like any word processor, but it uses the TeX engine for printed output and producing richly cross-referenced PDFs. It is stable and fully featured.
GNU TeXmacs is a free wysiwyw (what you see is what you want) editing platform with special features for scientists. The software aims to provide a unified and user friendly framework for editing structured documents with different types of content: text, mathematics, graphics, interactive content. TeXmacs can also be used as an interface to many external systems for computer algebra, numerical analysis, and statistics. New presentation styles can be written by the user and new features can be added to the editor using Scheme.
LavaPE is a programming environment for the experimental object-oriented programming language Lava. It replaces text editing with structure editing, thereby preventing all syntactic and many semantic errors. The pure point-and-click nature of Lava programming and the concise representation of programs as declaration trees with small chunks of executable code simplify programming, and ease comprehension.
GNU Moe is a powerful, 8-bit clean console text editor for ISO-8859 and ASCII character encodings. It has a modeless, user-friendly interface, online help, multiple windows, unlimited undo/redo capability, unlimited line length, global search/replace (on all buffers at once), block operations, automatic indentation, word wrapping, filename completion, a directory browser, duplicate removal from prompt histories, and delimiter matching.
FXiTe is an advanced cross-platform text editor built with the Fox GUI toolkit and the FXScintilla text widget. It features built-in syntax highlighting for 40+ languages, an embedded Lua scripting engine, macro recording and playback, multi-line regular expression search and replace, rudimentary ctags and calltip support, a flexible interface to external tools, and a built-in "message window" to capture the output of external commands such as compiler error messages, etc.