DISCUSS: Options for Sharing Data Across a WAN

From 'Phillipe' on the message board -

I am trying to find the best way to share data between four PCs in different homes, in different cities. My wife and three friends have started a small business together. They have a customer database that each of them must update when they talk to a client or when an order has been placed. The database is too big to be emailed (over 2GB), and burning a CD is cumbersome.

→ Discuss - Options for Sharing Data Across a WAN
→ See also - What is a WAN?
→ See also - What is a VPN?