I think more specifically the core state that drives an ACD abstracted into primitives any developer can manipulate.
Does that make sense?
Most ACD platforms provide work flow routing APIs so that third party applications can route tasks to the connected agents. Doesn't mean this is any less than an ACD with API's on it. Also task routing has become ubiquitous with the omni-channel multi-channel routing and CRM routing you see across all contact center vendor platforms.