E-XD++ Diagram Graphics Control is a 100% C++ / .NETbased Vector Editor, it ships with complete source codes, it contains the most popular vector graphics design, editing capabilities features.
http://www.ucancode.net
From the first version of E-XD++, it already has the full features on Visio Style flowchart Vector Editing, the current version of E-XD++ has performed its functions to extreme, basically, if you want to build any very professional Visio -Like flowcharts, network diagrams...