Is Agile BPM systems development possible?. Yes, it is possible.
This is the main reason why I like Intalio BPMS (BPMN, BPEL, BRE, ESB/SOA, BAM/BI, ECM and Portal integration and Rich Web RAD with Tibco GI).
Camunda Fox is "[...] an open source BPM platform. It helps you to build process-centric software solutions in Java." (http://fox.camunda.com)
Camunda explains its approach in this blogpost: Making the BPMN Roundtrip real
Activiti Cycle is collaborative approach in BPMS: "[...] The Process Cycle Layer identifies the layer on which business stakeholders, developers and IT operations people collaborate." (http://www.activiti.org/cycle.html)
Now, Camunda Fox (Free/Open Source project) is integrating and aligning to Activiti Cycle (http://www.bpm-guide.de/2010/08/27/done-first-activiti-cycle-preview-out) .
On 1st of september, Activi 5.0.beta1 was released containing the first Camunda contribution! (http://processdevelopments.blogspot.com/2010/09/activiti-50beta1-rocks.html)
I will follow evolution of this interesting initiative and hope to write soon on this and even maybe a comparison with the Intalio BPMS approach.