Draw.To is a basic online drawing tool. They write about themselves as:

Draw anything you like and share it instantly.

Create and share simple drawings — like those you do on a napkin in real life. Draw for fun or to communicate an idea. When you’re done you can share your drawing with a single click.

* 100% free — no signup required.

* Share drawings on Twitter, Facebook, email and more!

* Embed drawings in your blog or website.

* Add to existing drawings.

* Works in your web browser, no downloads required.

* Also works on iPhone, iPad and iPod Touch.

I have lists of other online drawing tools here.