1. Use some common php forum package like phpbb and mysql as database
2. Use facebook account as login account, no need for user to register another account and login in this system
3. User can subscribe the category he has interest (e.g. Pets - dogs). User can subscribe/unsubscribe categories anytime.
4. Multi language is supported, including both the user interface and the category name
5. User can select the language, default is based on their country registered in facebook
6. User can post topic on the category they have subscribed. They can choose either (1) only viewed and answered by friends or (2) only viewed and answered by friends and friend's friends. No strangers can view or answer topics
7. System will send email to users every day if there is new topic posted by their friends or friend's friend on the categories they have subscribed
8. System can allow user to invite friends to install this system
9. User can suggest new category (e.g. electronic product - ipad)
10. source-code is required
Please provide previous similar facebook app for reference.