What's the SiteWorx/OS project file extension?

Project files end with .ves. A backup is written as .~ves next to the project file every time you save. To use the backup, enable file extensions in Windows File Explorer (View → File name extensions), right-click the .~ves file, choose Rename, and remove the ~ from the extension. Save frequently — like Excel, in-memory data is not written until you save.