The Wordpress Administrator Dashboard is your central place to control your site. But if often gets cluttered with unnecessary stuff. For websites that have many users, its great to use that space to share to-do lists, website manuals, or general banter.
My preferred plugin for this is WP Dashboard Notes. Its elegant and easy - however you will need this use this snippet to clean up all the other junk (or just hide them per each user in Screen Options).
Here are some multi-user sites which have benefitted from the use of dashboard notes.