Which AWS service is always available free of charge to users?

Explanations:

Amazon Athena charges based on the amount of data scanned per query, and users incur costs as they run queries on their data stored in S3.

AWS Identity and Access Management (IAM) is always free and allows users to manage access to AWS services and resources securely without incurring charges.

AWS Secrets Manager is a paid service that enables users to store, manage, and retrieve secrets securely, with costs based on the number of secrets stored and API calls made.

Amazon ElastiCache is a managed caching service that charges based on instance type and usage, thus it is not free of charge.