You can use Diagraph to create diagrams, concept maps, SimuLink like block diagrams and mind maps using a user-extendable library of vector graphics (SVGs). The Prototype supports all basic editing types like dragging, scaling, rotating, connecting and creating annotations. All Operations are fully reversible and repeatable. There is the possibility to save and load snapshots online as well as offline. Additionally, the Prototype can handle multiple documents (copying, renaming, deleting) and supports importing and exporting of documents. Since Diagraph uses vector graphics, it can easily handle scaling and zooming of objects and the document.
A wide range of browsers is supported. However, if you want to use the full extend of Visio-Onlines features, you'll have to use Firefox 3.6+, Safari 5, Chrome 8, Opera 11 or IE9.