FCKeditor this HTML text editor brings to the web much of the power of desktop editors like MS Word.

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Demo

Damn Small Rich Text Editor - very small text editor.Built on top of well known JQuery library.

Download Damn Small Rich Text Editor

Demo

TinyMCE -Cross platform HTML WYSIWYG text editor .Supports templates, easy localizable and can be extended using plugins

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Demo

HotEditor - browser-based rich text editor that provides an advantage in simplifying the workload and providing options for integration to forum software

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Demo

WYMeditor - simple cross platform XHTML  web editor

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Demo

SPAW Editor is a web based in-browser WYSIWYG editor control enabling web site developers to replace a standard textarea html control with full-featured, fully customizable, multilingual, skinable web based WYSIWYG editor.

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Demo

My coworker wrote a interesting silverlight tool ,which allows to you test and play with string formatting syntax.Or you can use it as a interactive online reference when you deal with strings and localization.

Check out string format tool