There is an urgent need for novel programming abstractions to leverage the parallelism in modern multicore machines. We introduce S, a new domain-specific language targeting the server-side scripting of high-performance RESTful Web services. S promotes an innovative programming model based on explicit (control-flow) and implicit (process-level) parallelism control, allowing the service developer to specify which portions of the control-flow should be executed in parallel. For each service, the choice of the best level of parallelism is left to the runtime system. We assess performance and scalability by implementing two non-trivial composite Web services in S. Experiments show that S-based Web services can handle thousands of concurrent client requests on a modern multicore machine.