Lean Canvas is a business brainstorming tool developed by Ash Maurya. It is based on the famous Business Model Canvas. Both can be useful in their own way especially if you are trying to work out through the fundamentals of your startup.
As I like to use Google Docs for collaboration I ported the Lean Canvas as a Google Docs document. It is free for you to use. Just make a copy and go. There is also an implementation of a Kanban table for those interested.