I'll be absolutely shameless and plug our two services, Momentomail and Wormwall (http://www.kymalabs.com). Momentomail is a bit more mature since it's older. But when we first launched it, the entire site wasn't much more than a login page and the "Schedule an email" interface.

We made Lifehacker (after only adding a couple more things) not too long after that.

Wormwall likewise is about as basic a web authoring system as you can get. A WYSIWYG editor and a publish button. Nothing fancy.

We have well over a thousand users now.