I researched Signavio, and found out that it is based on Oryx editor. Oryx is an open source project, and has BPMN2.0 fully implemented. The schema created using the Oryx editor can be exported as BPMN 2.0 xml, or XPDL 2.0. Here is the main url for the project: http://bpt.hpi.uni-potsdam.de/Oryx/WebHome.