[update] Dassault Systemes purchased Matrix One about 10 years ago. They still use their Graph based DB kernel in many of their products. From my understanding, this DB kernel was written in the early 90's and targeted PDM (Product Data Mangement). They now target a broader category of PLM (Product Lifecycle Management). Again, there is no way to purchase their Graph DB Kernel last time I checked which is a shame because its so awesome to develop with :(