This blueprint can then serve as a base for developers to fork and integrate into various applications. While I can't directly access external documentation due to my current limitations, I can draw on principles from widely accepted system design approaches to help you outline a blueprint for a scalable and robust chat system. Here's a high-level overview:

• User Management: Registration, authentication, and user profile management.
• Contact Management: Adding/removing contacts or friends.
• Instant Messaging: Sending and receiving messages in real-time.
• Group Chats: Creating groups, adding/removing members, group messaging.
• Message Broadcast: Sending messages to multiple users or groups.
• Notifications: Real-time notifications for new messages or events.
• Media Support: Ability to send and receive media files (images, videos).
• Message History: Storing and retrieving past conversations.
• Search: Finding messages, conversations, and contacts.

• Scalability: Support a growing number of users and messages.
• Performance: Low latency for message delivery.
• Reliability: High availability and fault tolerance.
• Security: Ensuring data privacy and secure communications.
• Maintainability: Easy to update and maintain.

• Clients: Web, desktop, and mobile applications.
• Server: Backend services handling business logic, database interactions, and client communications.

• Web Server: Handles HTTP requests and serves the client applications.
• Application Server: Business logic, user/session management, and message processing.
• Database Server: Stores user data, messages, and system logs.
• File Storage: For media files and message attachments.
• Notification Service: Manages and dispatches notifications.
• Search Service: Indexes and searches messages and contacts.

• WebSocket: For real-time bidirectional communication.
• HTTP/REST API: For non-real-time interactions like user registration.

• Microservices Architecture: Splitting functionalities into microservices for better scalability and maintainability.
• Load Balancing: Distributing client requests efficiently to prevent any single point of overload.

• NoSQL Database: For scalability and flexibility in handling unstructured data like messages.
• Data Sharding: Distributing data across multiple databases to improve performance and scalability.

• In-Memory Data Store: Like Redis for caching frequently accessed data such as user sessions and active conversations.

• End-to-End Encryption: Ensuring that messages are only readable by the communicating users.
• Authentication and Authorization: Secure access control mechanisms.

• Containerization (Docker): For ease of deployment and managing dependencies.
• Continuous Integration/Continuous Deployment (CI/CD): For streamlined development and deployment processes.

This blueprint provides a foundational structure for a chat system that can be customized and scaled according to specific application needs. Each component and consideration can be further detailed during the development phase, based on the technology stack and infrastructure choices.