Let's make web-site for pure P2P interaction.
I started to study Drupal to make p2p market place.
There are some ways to let communities interact independently from each other and private services.
Every community run its own Drupal site with local market place and shares its resources (ads, projects) with other Drupal instances of other communities.
They can do this by:
RSS/Atom. RSS feeds enable publishers to syndicate data automatically.
D2D ("Drupal-to-Drupal") is a module to built-up a network among Drupal instances using cryptography and XML-RPC. An instance holds a public/private key pair allowing messages to be encrypted and/or to be signed. The concept of friendship among Drupal instances is introduced. Instances can send friend requests, accept friendship requests and also terminate friendship. https://drupal.org/project/d2d
For accounting best fits - Ripple - decentralised p2p accounting system based on mutual trust. As currency unit it is good to use independent and non-infation measure of value - minimal wage, hourly minimal wage.
Started groups in social networks:
https://www.facebook.com/groups/p2ptimebank
http://vk.com/bank.vremeni