Contact Manager

I need a web application that can aggregate several contacts together. I am going to call this application contact-manager in my further description of the requirements. They are as follows: 1. The application must be able to import contacts from a) LinkedIn, b) Google Contacts and c) Xing for now. The architecture design should consider an extensibility for other potential social platforms. The import mechanism should use the APIs provided by the mentioned plattforms. One-way synchronisation is sufficient (e.g. data from linkedin to contact-manager, not the other way round). I don't want the user to export their LinkedIn contacts to an excel sheet and later on manually import it to the conctact manager. The contact-manager should be able to authenticate against LinkedIn, etc. so the contacts can get imported seamlessly. 2. The contact-managers front-end must run on Android devices for now. It must not mess with the phones contact. Also it must be usable via browser (Chrome is sufficient). The back-end design should consider an extension to iOS later on, however an iOS based front-end is not required for the moment. 3. The back-end design and architecture of the application should consider a multi-user environment, although this is not required for the moment. It is advisable to provide a REST API that allows for communication betweend front and back-end. 4. The contacts should be made available offline on the front-end (cached), but the main-storage should be on the back-end. 5. The contact-manager must support a function so "tags" can be added to each contact. Also a free-text field should be available on each contact. The user must be able to add and modify contacts, add & remove tags, modify all the contact details, etc. 6. The contact-manager should provide a fulltext search function including the tags and all available information. 7. All contact fields (attributes) available via LinkedIn and co. should be made available and editable within the application. This are the requirements as of now. As due to the nature of the difficulty of defining requirements I am pretty sure there are open questions. I am going to add them as soon as I was able to clearify them. I am looking forward to your bids and questions. Thanks for your time and professionalism. Matthias