Not to come across as a Microsoft fan boy (I work with MS focused Shops mostly), but the MS Whiteboard tool is pretty solid for a simple collaborative tool that

Not to come across as a Microsoft fan boy (I work with MS focused Shops mostly), but the MS Whiteboard tool is pretty solid for a simple collaborative tool that has worked well in small teams when I've used it. I'm sure there are similar tools with more advanced features but sometimes simplicity is best, such as a real white board.