Updated: June 20 2008

Galaxia is an activity-based workflow application, where the processes and the workflows are made of dynamic activities that must be completed to finish a task. Contrast this with a procedural system where each step in the process must be completed in order, and the power of this application becomes clear.

OpenFlow - OpenFlow is an extremely flexible workflow engine, that enables rapid development of web based, "workflow-oriented" applications.

CuteFlow is an open source workflow system.for circulation of documents.

eZCompents has workflow capabilities in the Workflow component that provides:

... a virtual machine that executes workflows represented through object graphs. These object graphs can be created programmatically through the software component's Workflow Definition API. Alternatively, a workflow definition can be loaded from an XML file. Object graph and XML file are two different representations of a workflow definition that uses a backend language built on the workflow patterns.

PHPRules is a "lightweight, forward-chaining inference engine based on the "Rule Archetype Pattern" described in the excellent book Enterprise Patterns and MDA: Building Better Software with Archetype Patterns and UML".

Last, but far fron least, are the Drupal Workflow and Drupal Workflow-NG modules. In my limited experience, they are both powerful and easy to use relative to other wokrlfow engine implmentations. Note: one of my never-ending ( or is it never-beginning ? ) projects is a demo of the Drupal modules. Also see Links::Drupal and Workflow Management and Links::The Drupal Rules Engine Project.