AWS SNS (Simple Notification Service)
Pub-sub fan-out — publish to a topic; AWS delivers to all subscribers (SQS queues, Lambda, HTTP, SMS, email, mobile push).
Launched 2010. Standard topics are at-least-once, FIFO topics (2020) guarantee order and exactly-once deduplication. Subscription filter policies let subscribers select which messages they receive via attribute matching.
Common pattern: SNS → SQS fan-out = "send the same message to multiple queues consumed independently". EventBridge is the successor when more routing is needed.