LINK TO SITE
This Web "whiteboard" is touch-friendly online whiteboard app that lets you use your computer, tablet, or smartphone to easily draw sketches, collaborate with others, and share them with the world.
Works on all modern browsers, no installation needed.
The free version is a bit limited: creations can't be saved, and only basic tools are available, but all participants can contribute. If you'd like to save your creation, I suggest taking a screen shot and saving it that way. Paid plans are available.