The installer file for the free Windows version typically appears as Zoiper_Free_3.15_Setup.exe .
What are you using? (Windows, Mac, or Linux?) Zoiper 3.15 Download--
Download Zoiper 3, a free VoIP softphone. Zoiper 3 Providers. :: Zoiper. How To Install Zoiper On Linux 3 Sept 2018 — The installer file for the free Windows version