a textile editor,
built over HTML5 canvas
I'm pretty sure that textile is the right way to produce content for the web, and that WYSIWYG editors are bad for your website. But editing a large chunk of textile using a textarea is not fun. I usually use Textmate to edit textile content, and wanted to reproduce the same feeling inside a browser.
The best online text editor is currently Bespin and I gave it a try. Unfortunately, the current state of bespin make it pretty difficult to embed the editor itself in a standalone way. Moreover I needed specifics features like 'soft wrap' that is totally required to edit some textile content.