TinyEditor is a lightweight (8kb) JavaScript WYSIWYG editor that is free to use in both personal & commercial projects.

It is a standalone script (does not require any JS frameworks) & converts any given textarea to an editor

The can be easily customized by updating the parameters (like removing some of the controls). And it is possible to style it via CSS:

TinyEditor can be resized, a starting content can be defined, set to generate HTML or XHTML code & more..

MooEditable is a MooTools plugin that instantly converts a textarea field into a WYSIWYG editor.

It has a slick interface & comes with only the frequently used items like text formatting, lists, inserting images/links & undo/redo.

The plugin can also switch between design & HTML modes.

If you'd like to improve it further or customize to your needs,  It has a very detailed documentation.

WMD is a lightweight HTML editor which is ideal for blog comments, forum posts & basic content management.

It can be implemented into any textarea with one line of code & with an extra line, live preview functionality can be implemented.

This is not a WYSIWYG editor. Rather, it is a WYSIWYM Markdown editor (what you see Is what you mean).

WMD produces clean semantic HTML, leaving presentation details like fonts and colors up to style sheets.

Markdown: a simple markup language that’s as easy to read and write as plain-text email.

FCKeditor, one of the most popular free WYSIWYG editors around now has a new version with more features & a lighter name: CKEditor.

WYSIWYG editors generally load slow due to the highly-used JavaScript. One of the best things CKEditor offers is the seriously improved perfomance to eliminate this problem.

Also, it is now an accessible script in compliance with the W3C WCAG & the US Section 508.

CKEditor offers a rich & powerful integration and interaction API. The editor is also totally plugin based & can be extended/modified in all senses to fit every need.

With a new user interface based on a fresh skin which is colorful like a chameleon, you can change its color to match your needs.

Xinha is a powerful & open source HTML (WYSIWYG) editor.

It is a community-built script presenting various options for max. customization.

It has lots of plugins that can be activated like:

• Character counter
• Find & replace
• Image manager
• HtmlTidy
• Spell checker & more.

It is possible to configure which features/menus to be displayed, whether coding inside will be permitted or not & almost anything that may be needed.

WYMeditor is a free XHTML editor script that generates perfectly structured XHTML strict code.

It doesn’t provide shortcuts for styling the fonts, colors, etc. For this reason, it calls itself WYSIWYM (what you see is what you "mean").

This is a very nice feature to prevent novice users from breaking the styles of webpages (which happens most of the time).

WYMeditor is 100% JavaScript, has a skin support via CSS for customizing it and multilingual.

Its makes integrations easier with the API/plugin support provided.

Corpocrat is presenting 2 simple & handy editors:

• Markup editor
• BBCode editor

They both convert a textarea into an editor & they are lightweight (<5kb).

Links & images are inserted with an alert window rather than a HTML popup.

And, they are free to be used in both personal & commercial projects.

SmartMarkUP is a flexible & lightweight JavaScript library that turns any textarea into a markup editor.

It can be configured to edit HTML, CSS, XML, Wiki syntax & BBCode.

The library is unobtrusive & degrades gracefully if JavaScript is disabled.

SmartMarkUP has a simple and powerful API. Styles can be changed, new markups can be implemented, extra buttons and submenus can be created & more.

It also supports keyboard shortcuts for easier usage & has add-on support like color picker, search-replace, special character picker (and new ones can be created).

Free Rich Text Editor is a feature-rich JavaScript WYSIWYG editor.

It can be implemented to any web application easily & no programming experience required.

It outputs XHTML compliant code & works in all major browsers.

Editor lets you to switch between the design, HTML code & preview modes just like a desktop WYSIWYG application.

jWYSIWYG is a jQuery plugin for creating inline content editors easily.

It turns a textarea into an editor via a simple function below:

$(function()
{
    $('#wysiwyg').wysiwyg();
});

It has very simple features that makes it suitable to be used in contact or comment forms & similar.

jWYSIWYG is lightweight (7kb packed) & provides the ability to add custom controls, like adding a "line break" function.