Balsamiq Lync CWE Shape for Mockups
If you have Balsamiq Mockups you can download the shape and just start using it.
If you don’t have Mockups you can download a fully functional trial and give it a go. It’s brilliant for getting ideas across to people quickly, and doesn’t look finished or polished, so people don’t get confused with actual working software (!) and aren’t afraid to criticise it.