Action Cable is Rails’ built-in framework for WebSockets, enabling real-time features such as chat, notifications, and live updates. It integrates seamlessly with ActiveRecord, allowing broadcasted data to flow directly into client-side subscriptions. 

Setup involves creating channels, subscribing clients, and broadcasting from controllers or jobs. It supports Rails 6, 7 and 8 on Ruby 3+ and is actively maintained as part of Rails itself. Strengths include tight integration and ease of use for real-time features, while weaknesses are performance limitations at very large scale compared to specialised WebSocket servers.