Free software from github.com/FreeFaxDesk/faxdesk is signed by SignPath Foundation, with a certificate provided by SignPath.io. Builds are made by GitHub Actions from a tagged commit of the public repository; nothing is built by hand.
FaxDesk does not transfer any information to any service other than the fax provider the user configures (for example Phone.com), and only to send and receive that user's faxes. The program never phones home: no telemetry, no update checks, no analytics. The licence key for the whole-office option is verified on the user's own PC.
Right-click FaxDesk.exe > Properties > Digital Signatures. The signer should read SignPath Foundation, and the file hash should match the one on the GitHub Release.