1. A method comprising: at a multi-tenant work distribution platform that provides a work distribution service for a plurality of external systems, controlling at least one processing unit of the work distribution platform to: assign a priority to a first work item of a first external system, the first work item being received via a RESTful work item Application Programming Interface (API) call request, the priority being assigned based on work item attributes of the first work item and a workflow instruction corresponding to workflow information specified by the first work item, the workflow instruction being provided by the first external system via a RESTful Workflow API; assign a worker to the first work item based on: the priority of the first work item, the workflow information, and worker state managed by the first external system via a RESTful Worker API, the worker state including worker attributes, wherein the first work item is generated by the first external system, and the workflow instruction is managed by the first external system.