Disclaimer: Portal Builder and External Participant were developed for IBM Business Process Manager 8.5.x and have not been tested with Business Automation Workflow and are provided by IBM to its customers AS-IS at no cost and without support.
IBM acquired the Portal Builder and External Participant toolkits in 2016 from Salient Process.
Find toolkits for download along with available documentation here
Learn more about the latest Business Automation Workflow capabilities here and take a peak/try it out