Definition from the Metacollab encyclopedia.
"A collaboration tool is something that helps people collaborate. The term is often used to mean collaborative software, but collaboration tools were being used before computers existed, a piece of paper can for example can be used as collaboration tool.
Everything that helps to solve a predefined task together in a group more easily is an effective collaborative tool. Collaboration means in this context working together to fulfill a shared, collective, bounded goal." (http://collaboration.wikia.com/wiki/Collaboration_tool)