Documentation Redirect
(kafka.apache.org)
referenceKafka docs tree: key concepts, APIs, configuration, design, operations, security, Connect and Streams
Apache Pulsar
(pulsar.apache.org)
toolmulti-tenant pub-sub plus streaming with geo-replication and tiered storage, top-level ASF project
NATS.io
(NATS.io)
toolsingle-binary pub/sub, request-reply and JetStream persistence from cloud to edge, open source
ZeroMQ
(zeromq.org)
toolbrokerless sockets carrying atomic messages over TCP, IPC and multicast; pub-sub, push-pull, LGPL
Overview - Knative
(knative.dev)
referencescale-to-zero serving and event routing layered over Kubernetes, with the concepts behind it