Which VistA

VistA is available form the United States Federal Government via a Freedom of Information Act request. The sourcecode that you get from this request is in the public domain, which means that it can be used for a product using any license. Here is a list of products based on VistA, what their licenses are and links to further information about them. The version of VistA that you can get directly from the Veterans administration is often called FOIA VistA to distinguish it from the other products on this list.