Including Dia in this series is just a bit of a stretch, because it is not a conventional "vector graphic editor". Instead, Dia operates at a somewhat higher level of abstraction. But since that abstraction is very appropriate for dataflow diagrams (such as the one I picked as a comparison project), I think it's important to note what it can do. Dia is very useful, but it's sometimes frustrating, because the idea of it suggests expectations well beyond what it can actually do.