Editing YAWL work flows with the web based Oryx process model editor is the goal a project I am currently working on.
Oryx was developed by students at the Hasso-Plattner-Institute (HPI) and uses JavaScript and SVG to provide process editing with a web browser.

Currently it is possible to export and run Oryx diagrams as a YAWL workflow by using an extension of the BPMN 1.2 stencil set. (see BPMN to YAWL and YAWL Integration to Oryx) This specification could be used as a starting point for further modeling with the native YAWL editor. Useful if there are already complex BPMN processes in your organization, that should be supported by a workflow engine.

YAWL workflow imported to Oryx

This project is going much further as, on a long term perspective, it aims to enhance Oryx with support for the whole YAWL specification. As the YAWL workflow system contains features that are hard to adapt to the Oryx process model editor environment, (e.g. custom codelets, worklets or the resource service) the control flow perspective will be implemented with higher priority than those special features. In the beginning, a YAWL specification should remain functional, as being imported and exported afterwards. Currently it is already possible to import simple workflows like the "Credit Rating Process", taken from the YAWL examples to Oryx. The source code is not yet released to the public, as this project is in an early stage. Feel free to contribute to this projects with your questions or proposals.