RMQTT is a production-grade, high-performance MQTT broker written in Rust, supporting MQTT v3.1, v3.1.1, and v5.0. It is deployed as a standalone binary (`rmqttd`) or as an embeddable library, and features a modular plugin architecture with 26+ built-in plugins covering authentication (HTTP, JWT), authorization (ACL), storage (RAM, Sled, Redis, Redb), bridging to external messaging systems (Kafka, Pulsar, NATS, ReductStore, remote MQTT), clustering via Raft or broadcast, and a rich HTTP API with an embedded Vue.js dashboard. The broker handles millions of concurrent connections, supports TLS, WebSocket, and QUIC transports, and includes advanced features like shared subscriptions, delayed publishing, flapping detection, topic rewriting, and system topic subscriptions for observability. The architecture is based on the Tokio async runtime, with per-connection tasks, bounded message queues, and a plugin hook system that allows extending the broker without modifying core code. Key entry points include `rmqtt-bin/src/server.rs` for binary startup, `rmqtt/src/v5.rs` and `rmqtt/src/v3.rs` for protocol handling, and `rmqtt/src/context.rs` for runtime orchestration. External dependencies include gRPC (via Tonic) for inter-node cluster communication, Sled/Redis for persistent storage, and various client libraries for bridges (rdkafka, pulsar, nats). The broker is extensively tested with a custom test harness (`rmqtt-test`) that includes >600 functional, stress, and chaos tests, many reproducing real GitHub issues. The codebase demonstrates strong engineering practices: a clean plugin lifecycle, efficient topic trie for wildcard matching, reusable utility crates (`rmqtt-utils`, `rmqtt-codec`, `rmqtt-net`), and a comprehensive test framework that manages broker processes and configs. The dashboard and HTTP API provide operational tooling for client management, metrics, and plugin configuration. While the project is actively maintained, the large number of feature flags and optional storage backends create some configuration complexity, and a few tests rely on hardcoded ports or timing, which can be brittle. Overall, RMQTT is a solid, extensible MQTT broker suitable for IoT and real-time messaging use cases.