Who developed or what parties developed the vistaa and worldvista ehr?

VistA was developed by the United States Department of Veterans Administration. The first version was developed in the late 1970s.
WorldVistA EHR was developed from the public domain VistA code at the time (2002) and has been updated to new code since then.

I know this because I am one of the parties that worked at the DVA and co-founded the WorldVistA organization. Our website is at http://www.worldvista.org if you want more information. (or send me an e-mail at [email protected], phone is 713-870-3834 )