Drools - Drools introduces the Business Logic integration Platform which provides a unified and integrated platform for Rules, Workflow and Event Processing.
Camunda - The Universal Process Orchestrator
Imixs-Workflow - Imixs Workflow is a BPM Framework with the goal to reduce the complexity of business applications.
jBPM - jBPM is a flexible Business Process Management (BPM) Suite.
Inspex - Detect changes within your data stream and get alerts in 4 easy steps.
ProcessMaker - ProcessMaker is an easy to use BPM and workflow software solution. It is used to design, automate, and deploy business processes of any kind.