If you want to doodle an idea or a plan in a semi-formal setting by tweaking, experimenting and discovering new concepts, then a canvas is a useful, quick and easy way to do so.
There are a few sites available offering such a service. The one I recommend - only because it has more canvases instantly available - is:
Firstly, select an appropriate canvas for your requirements. Then add items, which look like a Post-it, in the relevant sections. You have color coding options, which I use for order of importance. If you have put it in the wrong section, you can move it around. You can share it with other people, too, if you want. The interface is easy to understand.
One other site that is worth a look is:
Note: Google Docs has some interesting stuff about this, too.
Let me know what you think.