Linphone is an open source and free VoIP service that allows users to make and receive audio and video calls, as well as send and receive instant messages over the Internet. It is designed to be easy to use, fast, secure, and reliable. The app is available for Windows, Mac, Linux, iOS, and Android devices. It also offers encrypted communication, which makes it a great choice for businesses. With Linphone, users can make free calls to other Linphone users, as well as make and receive calls to/from landlines and mobile phones using the SIP protocol. The app also supports conference calls and allows users to share files and photos. Other features include call forwarding, call recording, call history, call transfer, and more.
Skype is not a SIP client. It is an end-to-end VoIP type software, but you cannot use it to register to SIP servers ...
Linphone is just a client, which can connect to multiple services (even an asterisk server hosted on your local network). Skype is a full service, the client cannot be configured to work with any service other than Skype.
Linphone provides a SIP client that is compatible with many standards-compliant VOIP services. Wire is not a SIP client, but provides access to a proprietary VOIP network.
Discontinued empathy is not currently maintained. The latest version, 3.25, released in August 2017, can still be downloaded from the official website.
Xabber is not a phone solution, only instant messaging.
Discontinued Possibly suspended. The application has not been updated since November 30, 2014.
CSipSimple works fine with a UK Sipgate account and has no reason to use anything else. The bad news is that it only works with Android phones.
Signal
Skype
Hangouts
Wire
Jitsi
Conversations
Empathy
Imo
Ekiga
Xabber
YakYak
Zoiper
CSipSimple
Nimbuzz
MicroSIP
Coccinella
3CX Phone System
X-Lite
Telephone
SeaFour.club
Linphone provides an interoperable SIP client with many standards-compliant VOIP services. Skype is not a SIP client, but provides access to a proprietary VOIP network.