Diagrams and charts are useful for people coordinating in a group. I have written previously about Google charts, Lovely Charts and more recently about Creately. On similar lines, Diagram.ly also allows users to create diagrams and share using your Google or Google Apps account and integrate it with your Google Drive account.
The diagrams can be created with many predefined elements based on various categories. For example there are many clipart images, flowchart styled arrows and branches to choose from.
A diagram can be saved on your desktop from the browser itself as an XML file.
More important it can be shared with your friends either by embeding it on a webpage or even sharing it via a URL.
My favourite part of Diagram.ly is that is can be integrated with Google Drive, allowing me to share a particular diagram with anyone form my Google contacts.
It is free and one does not even have to sign-in or register unless integrating with Google Drive. Try out Diagram.ly and drop in your comments.