What is VistA Really

VistA is a Electronic Health Record programed by Federal (US) employees working for the Veterans Association for several decades. Because it was developed by Federal Employees, it is available under a Freedom of Information Act (FOIA) request. The version of VistA available directly from the US Government is usually referred to as FOIA VistA. 

Licensing of FOIA VistA

It is a common mis-conception that VistA is "Open Source" software. Technically, VistA is in the public domain. As a result VistA can legally be the basis of both proprietary software and Free and Open Source Software. FOIA VistA does meet the definition of "Free Software".

The fact that VistA can be proprietary software AND free software creates an ongoing tension between different portions of the VistA community. For instance WorldVistA has a policy of releasing software under the GPL. The GPL is a "keep it free" license that prevents proprietarization. Some proprietary VistA vendors support other licenses that allow for proprietarization.

What do you mean by...

The first barrier to really understanding VistA is one of overlapping vocabularies. Often people who are technically savy have a more difficult time with this than those with less technolgical experience. This problem is directly related to the age of VistA.

VistA is written in MUMPS