Which AWS service is primarily focused on enabling developers to build and run complex workflows?

AWS Step Functions is designed specifically to help developers build and run complex workflows by allowing them to coordinate multiple services into serverless workflows. It provides a visual interface to define state machines that dictate the sequence and conditions of these workflows, which can integrate various AWS services seamlessly. This feature enables developers to create intricate business workflows that can handle events, parallel processes, and error handling without the need for managing underlying infrastructure.

While AWS Lambda allows for running code in response to specific triggers, it does not focus on orchestrating workflows like Step Functions does. AWS Trusted Advisor is aimed at providing real-time guidance to help provision your resources following AWS best practices and is not workflow-centric. Amazon CloudWatch serves as a monitoring and operational data service but does not handle workflow orchestration or execution. Hence, Step Functions stands out as the go-to service for managing and executing sophisticated workflows in the AWS ecosystem.