[jfaucett]

I'd love to have a simple newsletter tool, with a backend administration interface that clients could use (WYSIWYG editor, etc).

[vtanase]

This sounds doable, shoot me an e-mail and we can see how simple is simple for you. :)

[derpmeister]

Parent is asking for a spam program, don't fall for it. Sending bulk email isn't trivial at all and there are already good solutions for it such as Mailchimp and Campaign Monitor.