ZeroMQ (also known as ØMQ, 0MQ, or zmq) looks like an embeddable networking library but acts like a concurrency framework. It gives you sockets that carry atomic messages across various transports like in-process, inter-process, TCP, and multicast. You can connect sockets N-to-N with patterns like fan-out, pub-sub, task distribution, and request-reply. It's fast enough to be the fabric for clustered products. Its asynchronous I/O model gives you scalable multicore applications, built as asynchronous message-processing tasks. It has a score of language APIs and runs on most operating systems. ZeroMQ is from iMatix and is LGPLv3 open source.

Kafka

Event Storming exercises help you to figure out which domains you have in your system and give you a clear view on the different events. You can then formalize events and commands.

Ideas about Event Sourcing have been spreading. Functional programming gained popularity in parallel with event sourcing. Event sourcing is a natural functional model. Every state is a left fold of your previous history.

A lot of other things also pushed Event Sourcing forward:

Cloud computing
Popularity of Actor Models
Microservices
BAD THINGS
Some people see CQRS as a full-blown architecture, but it’s not. This is wrong. CQRS and event sourcing is not a top level architecture. You cannot build an Event Sourced system. Instead, you end up into building a monolith which is event sourced internally. Event sourcing is simply not a good solution to every problem. For example, once you deal with immutable events, you need to think about corrections to data. Whenever a user corrects a value and hits the save button again, you would need to have an event for that and it would be too complex to handle.

"RabbitMQ is the most widely deployed open source message broker"

Watermill is a Golang library for working efficiently with message streams. It is intended for building event-driven applications, enabling event sourcing, RPC over messages, sagas and basically whatever else comes to your mind. You can use conventional pub/sub implementations like Kafka or RabbitMQ, but also HTTP or MySQL binlog if that fits your use case. It comes with a set of Pub/Sub implementations, which can be easily extended by your own implementations. Watermill is also shipped with a set of standard tools (middlewares) like instrumentation, poison queue, throttling, correlation and other tools used by every message-driven application. Our goal was to create a tool which is easy to understand, even by junior developers. It doesn't matter if you want to do Event-driven architecture, CQRS, Event Sourcing or just stream MySQL Binlog to Kafka. Watermill was designed to process hundreds of thousands of messages per second. Every component is built in a way that allows you to configure it for your needs. You can also implement your own middlewares for the router. Watermill is using proven technologies and has a strong unit and integration tests coverage for the critical areas.

Emitter is a real-time communication service for connecting online devices. The Publish-Subscribe messaging API is built for speed and security.