Windows: If you aren't happy with the limitations of the web's plain text boxes, Text Editor Anywhere lets you edit text from any program in the editor of your choice.Some websites or programs have OK text editors, but chances are you already have a favourite on your system. If you'd rather write emails with the power of Office behind you, or write blog posts with the HTML markup of Notepad++, Text Editor Anywhere will let you do so.
Just add your favourite text editors to Text Editor Anywhere's database, and when you want to write inside one of them, just hit Text Editor Anywhere's hotkey and pick your editor from the list. It will automatically take any text you've already written and start a new file for you. When you close that editor, all your text will be transferred back to the original program seamlessly.
Text Editor Anywhere is a free download for Windows only.