Cross-platform Social product. Please respond with stack proposal.

[re-posting project I posted 2 days ago with updates] Hi there, Please respond with a brief proposal of the stack you would implement to deliver the required features below. I will provide all product design, interaction design, UI design... everything that isn't code. I need this to work on iOS, Android and desktop (with a different UI). I'm open to web view for iOS, Android. Functionality: - users can sign up (auth using fb, tw, google) and create account - users can post piece of content consisting of 118 char heading, 1000 char body, image, location on map, timestamp - users can link that piece of content to a business or organisation near to their current location / by searching (using Foursquare/Google Places/other API) - users can view content posted by other users - content shown to users filtered to show them relevant content based on location / content they have posted - user profile pages showing their posted content - businesses / organisations can sign up, create profile for their business / org, view content posted for their business / org - business / org pages public, show all content for those businesses / orgs - businesses / orgs can reply to content posted -- pieces of content show original pieces of content + reply - reply consists of 118 char heading, 1000 char body, timestamp, and status string selection - users can +1 pieces of content, -1 on pieces of content, comment on pieces of content, share pieces of content - users / businesses / orgs can flag pieces of content as inappropriate - users / businesses / orgs get notifications when people +1, comment, flag pieces of content