jBPM is a flexible Business Process Management (BPM) Suite. It makes the bridge between non technical business users and developers.
Quartz is a full-featured, open source job scheduling service that can be integrated with, or used along side virtually any Java EE or Java SE application - from the smallest stand-alone application to the largest e-commerce system.
OSWorkflow is fairly different from most other workflow systems available, both commercially and in the open source world. What makes OSWorkflow different is that it is extremely flexible.
Together XPDL Workflow Server is an enormously flexible and extensible WfMC XPDL and OMG Workflow Management Facility compliant embeddable and / or standalone Java Workflow Engine.