Legend (formerly Moo.do) is a notepad, a to-do list, and an outliner, but with advanced features that make the cloud-based application much more useful than any of those tools would be on their own.
Email and IM are linear contextless communication tools. Messages pile up and get lost or become redundant. There's no way to keep track of who replied to what, or which version of the conversation is the newest.
kune is a social network where you can communicate, collaborate and share between equals, using different web tools: documents, calendars, chats, wiki, messages, tasks, forums, barters.