Help! finding a client

A while ago i read some where about a client that was released that would let you share files with your friends based on having their ip address and a key (kind of like a password/identfication thing) that you could generate. Does anyone know what program i am talking about or know of a program that his features like this? My friends and I are thinking of starting a small network between ourselves to share files with each other and our relative and whatnot. Or does anyone know of an easy way i would be able to set something like this up?

There are some clients like that, such as WASTE, Alliance P2P or Retroshare. A difficulty is to keep in touch with the others, especially when the members have changing ip-addresses or aren't online so often. WASTE is clean and simple, the classic from Nullsoft - but it's not exactly noob-friendly and you need to care about the network so it can survive. In contrast both Retroshare and Alliance P2P will assist you in finding together, the first even features a DHT to search for lost peers. Just have a look at them ; )