Coordinate Distributed Applications
The Step Functions free tier includes 4,000 free state transitions per month. All charges are metered daily and billed monthly. This service provides a way for you to visually connect pieces of your application when the pieces are serverless or otherwise stand-alone functions.
Managed Message Queues
Simple Queue service is a bundled solution. It runs on a server and uses storage for the queue. Thus, the two pieces combine for the pricing and utilization. You can get started with Amazon SQS for free. Accordingly, all customers can make 1 million Amazon SQS requests for free each month. Some applications might be able to operate within this Free Tier limit.
Managed Message Topics for Pub/Sub
There is a free tier that covers your first million push notifications (publishes and deliveries) every month. The notification service is similar to a queue. However, instead of a push and pop approach, it is a subscribe/publish model. In general, your application subscribes to a topic. Then, when a message appears on the queue, the application receives it and can process accordingly.
Managed Message Broker for ActiveMQ
The Amazon Message broker Free Tier includes up to 750 hours of a single-instance mq.t2.micro broker per month. The storage starts at up to 1GB of storage per month for one year on the free tier. All new AWS accounts are eligible to receive the 12 months of AWS Free Tier access. As always, you can check out the AWS Free Tier page for details.