In which framework do the developers no longer have to deal with capacity, deployments, scaling and fault tolerance, and OS?

Docker Swarm is a container orchestration tool that still requires users to manage the underlying infrastructure, including nodes, scaling, and OS.

Kubernetes is a powerful container orchestration system, but it requires users to manage the cluster nodes, install Kubernetes, and configure deployments, scaling, and fault tolerance, even if it automates many aspects.

Apache Mesos is a distributed systems kernel for managing compute resources, but like Kubernetes, it requires significant operational overhead for infrastructure management.

Serverless computing platforms, such as AWS Lambda, Azure Functions, or Google Cloud Functions, automatically handle all underlying infrastructure concerns including provisioning, scaling, patching, and fault tolerance. Developers deploy their code, and the platform executes it in response to events, charging only for the compute time consumed, thus relieving them from operational overhead.