Linphone is #1 in Top 10 SIP Softphones

https://www.linphone.org/

Linphone is an open source Voice Over IP phone (or SIP phone) that makes possible to communicate freely with people over the internet, with voice, video, and text instant messaging.

Positions in ratings

#1 in Top 10 SIP Softphones

Alternatives

The best alternatives to Linphone are: Zoiper, Asterisk, MicroSIP, Jitsi, 3CX Phone, Bria, Ekiga