filesharing
There are all sorts of ways to share things. After all, a computer is fundamentally a data copying machine. Networking them has but one purpose from the perspective of the 0s and 1s. Moving 'files' of data around is what computers do best.
It's a fairly primary use for networked computers to share files. The paradigm shift with peer to peer sharing is that it is decentralised. Technically, any home network or intranet will work this way unless a centralised server is established. However, to share files with strangers P2P, through the internet, is a kind of revolution. It's not really the technology itself that is so radical, but the culture of widespread use is. The world wide web put a visual face on all of these networks and so it is not surprising that popular applications are ones that integrate well with the web user.
There are innumerable ways to share files. Older methods include ftp, usenet, gopher... Newer techniques use instant messenger programs [IM aka chat] and direct connect to share one-on-one. Issues of file search indexing and the degree of openness of the network are tantamount to social organisation of the community.
With the new mass forms of P2P, the rules of the community dictate that to take, you must also give. Sort of an exchange / barter system, though usually not so strictly metered as money is. This model of multiplication ensures more copies than even mass distribution of consumerism could provide. It is a model of massive expansion. However, the expanse of data is ever empty ether, idea proliferation. A mathematically encrypted language of babel in Babylon? Zeros and Ones.
Alongside the development of the computer, collaboration in open source, or free software has been the norm. Commercial exploitation of computers, though now extremely popular, is kind of the new kid on the block from the machine's perspective. There is no doubt that this industrial acceptance has spread the use of computers far and wide. Yet, in the face of this expansion, P2P filesharing has presented an even more multiplying alternative to counterbalance the commerce. Free software development has both provided the means and tagged along for the popular ride. Post capitalist communities that share and work together on massively complex cutting edge art and technological projects are spontaneously forming.