The ArcGIS Workflow Manager API is the development platform for ArcGIS Workflow Manager. The ArcGIS Workflow Manager objects expose the full range of functionality necessary for creating, managing, and working with jobs. These objects were built using Microsoft's Component Object Model technology and extends Esri's ArcObjects framework. This API allows developers to customize the default ArcGIS Workflow Manager application, write an entirely new application, or create custom tools to manage jobs.
Another point of customization is the executables. In addition to those provided by ArcGIS Workflow Manager, developers can create their own executables to be run when a particular workflow step is launched, thus tailoring the workflow to a specific project or business process.