Matrix is an open source, secure, self-hosted, decentralized chat service used by organizations of all kinds.
Review Board can talk to Matrix, notifying any given Matrix channel when there are new review requests or updates to review, or new discussions on a review request that you might want to pay attention to.
Review Board 5.0+
Review Board 5.0 and higher include Matrix built-in. You can make as many configurations as you like, controlling which review requests can be posted for which teams to which channels. See the documentation on getting set up.
What else does Review Board do?
Review Board gives you the tools you need to keep your code quality high, helping you build better products for happier customers. It integrates with many services and tools, including chat services, code hosting solutions, bug trackers, code analytics, and more.
Power Pack enhances Review Board further, providing document review, report generation, improved scalability, and more for your whole organization.