Not sure what you might mean by the question... it would seem the answer is... "To collaborate with other members of a team (from two on up to a reasonable number 9? 15?) in order to complete a project."
Teams could be internal to a company, or consist of differing home business entrepreneurs, or hobbyists, or varying non-profit activists.
Why would they need the tools? They probably could get away with no tools other than post-its, a white board, or a large sheet of paper for group brainstorming if they were located in the same room (geographic vicinity). But the greater the physical distance and/or the greater the time period over which the project must be done, the greater the use for such tools.
Tools vary so much! Included are tools that facilitate project and task management jointly, tools that facilitate writing projects, tools that facilitate brainstorming, communicating, sharing materials, screen sharing, and more.
Here is a great list of tools. It's not my list but it is a good reference.
My goal is to find one or two very simple tools that facilitate what the group wants to do. The more complicated the tool, the less it will be used by some.