1. Frontend with Vue.js:
   

   User Registration and Authentication:

   • User registration and login.
   • Social media login options.
   • User profile management.

2. Product Listings:

   • Users can create, edit, and delete product listings.
   • Upload images for products.
   • Product categories and tags for easy search.

3. Search and Filters:

   • Advanced search and filter options.
   • Sort products by various criteria (price, location, etc.).

4. Messaging System:

   • In-app messaging between buyers and sellers.
   • Real-time chat with notifications.

5. User Ratings and Reviews:

   • Allow users to rate and review each other.
   • Display user feedback on profiles.

6. Notifications:

   • Notify users about new messages, product updates, etc.

7. Payment Integration:

   • Integration with payment gateways for transactions.
   • Escrow services for secure payments.

8. Geolocation and Maps:

   • Location-based services for product searches.
   • Maps integration for viewing product locations.

9. Favorites and Follows:

   • Allow users to bookmark favorite products and follow sellers.

10. Report and Flagging:

    • Reporting system for inappropriate content.
    • User-driven content moderation.

11. Responsive Design:

    • Ensure the app works well on various devices.

12. Admin Panel:

    • Backend admin panel for user management, content moderation, and analytics.

Backend (PHP):

1. User Management:

   • User authentication and authorization.
   • User profile management.

2. Product Management:

   • Create, update, and delete product listings.
   • Image storage and management.

3. Messaging System:

   • Manage user conversations.
   • Real-time chat handling.

4. Payment Handling:

   • Process payments securely.
   • Manage transactions and escrow services.

5. Search and Filters:

   • Implement efficient search and filtering mechanisms.

6. Rating and Reviews:

   • Store and manage user reviews and ratings.

7. Notifications:

   • Send notifications to users.

8. Geolocation Services:

   • Handle location-based services.

9. Reporting and Moderation:

   • Manage reported content.
   • Implement content moderation tools.

10. Analytics:

    • Gather data on app usage and user behavior.

11. Security:

    • Implement security measures to protect user data and transactions.

12. API Integration:

    • Integrate with external APIs (e.g., payment gateways, maps, social logins).

13. Scalability:

    • Design the backend to handle a growing number of users and products.

14. Backup and Recovery:

    • Regular data backup and recovery procedures.

15. Performance Optimization:

    • Optimize the application for speed and efficiency.

16. Documentation:

    • Thorough documentation for future maintenance and updates.