VistAcom functions as a limited e-mail client to allow you to choose the encrypted Continuity of Care record (CCR) that has been shared with you. The code used includes EWD Classic, which generates web-pages from MUMPS to allow easy access to the VistA data for a developer.
This VistA Extension is written in MUMPS, and are installed in a VistA system using KIDS. They are all add-ons to the VistA system, and use VistA's built in extensibility frameworks to integrate with the rest of the system. So, as add-ons, they do not change or restrict in any way the functioning of the rest of the VistA system.