Bonita
Bonita is a flexible cooperative workflow system, compliant to WfMC specifications, based on the workflow model proposed by the ECOO Team, which incorporates the anticipation of activities as a more flexible mechanism of workflow execution.

Bossa
Bossa is a workflow engine written in Java. The engine is very fast and lightweight, uses a very expressive Petri net notation to define workflows, does not require a RDBMS and is very simple to use and to integrate with java applications.

con:cern
con:cern is a workflow engine based on an extended case handling approach. A process is described as a set of activities with pre- and postconditions. An activity is executed when its preconditions are met. It manipulates the process item, thereby creating postconditions. The process flow is determined at run-time.

Freefluo
Freefluo is a workflow orchestration tool for web services. It can handle WSDL based web service invocation. It supports two XML workflow languages, one based on IBM's WSFL and another named XScufl that is under development as part of the Taverna Sourceforge project.

JBoss jBPM
JBoss jBPM is a flexible, extensible workflow management system. Business processes, expressed in a simple and powerfull language and packaged in process archives, serve as input for the JBoss jBPM runtime server. JBoss jBPM bridges the gap between managers and developers by giving them a common language : the JBoss jBPM Process definition language (jPdl).

JFlower
JFlower is workflow engine written in java, extendible with java plugins. The server parse xml document for execute jobs, and check conditions. The session data are stored on a database, so the server is fully scalable.

JFolder
JFolder (formerly PowerFolder) is a complete application creation and production solution. You can develop many applications without writing any code, even scripting.

Open for Business Workflow Engine
The Open for Business Workflow Engine is based on the WfMC and OMG specifications. The Workflow Engine is a member of the Services Framework, and is tightly integrated with the Entity Engine. It uses the entities found in entitymodel_workflow.XML for definition information and entitymode_workeffort for runtime storage. All changes to a process or activity are persisted real-time.

OpenWFE
OpenWFE is a fully open source work flow engine. It is implemented in Java, and is available under a revised version of the BSD license. OpenWFE not only features a workflow engine, but also a full fledged Business Process Management Suite.

OSWorkflow
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.