Systems and methods for a work distribution service. At a multi-tenant platform that provides a work distribution service for a plurality of external systems, a priority is assigned to a first work item of a first external system. The work item is received via a RESTful work item API call request. The priority is assigned based on work item attributes of the work item and a workflow instruction corresponding to workflow information specified by the work item. The workflow instruction is provided by the external system via a RESTful Workflow API. A worker is assigned to the work item based on: the priority of the work item, the workflow information, and worker state managed by the first external system via a RESTful Worker API. The worker state includes worker attributes. The work item is generated by the external system, and the workflow instruction is managed by the external system.