Create a trip sharing web backend, plus a web interface

Overview We are looking to set up a trip sharing service, where - Users can register independently / log in with facebook/twitter/other social network/microblogging services. - Friend and unfriend other users. - Create / invite / modify and delete travel plans and decide the level of sharing (private, to network, or public) - users could share travel plans, photos/videos, comments and emotions when travelling. Prepare for a push service where the app will prompt users when they reach their travel destinations to upload photos and provide comments. e.g. if the user reaches New York, it will prompt the user if he wants to see Statue of Liberty, maybe upload a pic, tag the friends on the same trip and maybe send out a twitter/facebook post, @ them or tagging them. Or they could also leave a comment / see other's comments about the place. - These promotions will be based on what type of attractions/activities the user has liked, browsed many times, or what his friends has liked, using intelligence. - They will also be able to get connected to other people via 3rd party plugins, e.g. login using facebook, find/invite friends on facebook/twitter, etc. - Trips, media and activities/localtions will have high quality display interfaces. - when building trips, the known locations/details can be based on third party information (google maps, foursquare, tripadvisor etc). - Trips can be shared publically. shared trip details can be 'liked' or bookmarked for future travel inspirations. We like the way Google+ on iPad displays images. - Users can 'like' or mark the locations or activities they most wanted, this will be collected at a place like 'my travel folder' or something like that. - we are still open for any recommendations for features and the right recommendations will get you more paid work to do. Other features are on the plan and the finished piece of work should be flexible for expansion. Highly quality code submitted gives more chance to get involved in the second phase of the project. Frontend will be based on a full HTML5 website / mobile APP. We are open for suggestions for backend's technology, preferably on open source.