AirBnB - House and Room Sharing at low prices. Most of the time lower then hotels.
Zipcar - Instead of owning cars you pay a monthly membership fee and share cars with others.
Coworing - Office space sharing. Allows small business to rent out small parts of offices instead of whole offices making it easier for small businesses to find places to rent and make rent.
Others:
Thredup: A baby clothing sharing community
Toygaroo: toy sharing community