The Internet is a worldwide meta-network of computer networks.
It can be an excellent medium for sharing of knowledge like internet-based projects like Wikipedia show.
Also sharing of other stuff can be organised via internet.
It can also be very useful medium for the collaboration of people that may be physically apart, distributed over the whole globe. It has enabled the emergence of a bunch of new collaboration techniques. (See wikis, message boards, virtual presence, ...)
Sharing Internet access can be done for example by setting Mashup-networks, so called wireless community networks. (See Freifunk for example)