The lovely Geraldine kindly sent me this link
It's a blog post about an idea for a tool that helps local communities share resources and reduce expenses using geolocation, interactive mapping and visualisation.
It also mentions other interesting sites like:
https://thesuperfluid.com/ Superfluid makes collaboration in social networks fair by enabling members to trade favors using a virtual currency
http://ushahidi.com/ Ushahidi is a non-profit tech company that develops free and open source software for information collection, visualisation and interactive mapping
and discusses the possibility of using this software for organising community based initiatives.
It's worth a look - I'd be interested to hear other people's thoughts.