Soft Phone

Open Source/Freeware 
 
 Zoiper - Branding for your business, Freeware, Support mobile and desktop (Linux/Windows/macOS) 
 Linphone - Open Source, Support mobile and desktop (Linux/Windows/macOS) 
 MicroSIP - Open Source, based on PJSIP for Windows OS 
 PhonerLite - Freeware, For Windows OS