A tribe would be synonymous to an individual start-up. "A network of people that help one another" would be an entirely self-forming group or collective of groups. What makes communism distinct is that there's a central organization directing the economics.

To use the old "steak and potatoes" analogy, if one person specializes in steak and the other in potatoes, there's capitalist efficiency there. But if there's a third-party saying "you with the steaks: you'll get those from this particular guy with potatoes. and you with the potatoes: vice versa.", that's when there's potential communist undertones.

Not that I have a problem with communism: http://news.ycombinator.com/item?id=1926047