The VA FileMan is the database management software which the entire VistA stack depends. It was written in the late 1970s by George Timson, and has been enhanced continually since then. There is a form of this same software, known as CHCS FileMan which is at the heart of the Department of Defense CHCS system, and other variants available.
The Indian Health Service does NOT maintain its own copy of FileMan. It uses the same FileMan as the VA.
There is also a version of FileMan developed by the Medsphere Corporation including enhancements to FileMan that have been added by George Timson in recent years.