I'm sure you can do it, the layout is powered by WebCola which has an example of a DAG: http://marvl.infotech.monash.edu/webcola/examples/downwarded..., greuler is more like a tool that provides the necessary methods to interact with the nodes/edges of the graph in a nice way
I am looking for a tool to construct a PERT visualization, but it require to be a activity-on-node type of graph
does Greuler allows to construct such type of graphs?