X-Lite is described as 'Combining voice calls, video calls and Instant Messaging in a simple interface, CounterPath's X-Lite helps you seamlessly transition from a traditional phone environment into the world of Voice over IP' and is a instant messenger in the social & communications category. There are more than 25 alternatives to X-Lite for a variety of platforms, including Windows, Android, iPhone, Mac and Web-based apps. The best X-Lite alternative is Jami, which is both free and Open Source. Other great apps like X-Lite are Jitsi Desktop, Conversations, Linphone and Psi XMPP Client.
Open source decentralized communication platform supporting secure end-to-end encrypted calls, messaging, group conferencing, file and media sharing, SIP compatibility, multi-device sync, and strong privacy, available across desktop and mobile systems.
Jitsi Desktop (previously SIP Communicator) is a legacy audio/video and chat communicator with full encryption, precedessor of Jitsi Meet .
Jitsi Desktop is not actively developed anymore: last version, released in October 2017, can be still downloaded from GitHub. Its successor is 
Jitsi Meet
Free, open-source, plenty of features such as MS Outlook integration, ability to connect to external directories such as LDAP and MS Active Directory ...
can connect to arbitraty VOIP providers
Conversations is a privacy focused, open source XMPP Texting [Jabber] client for Android 4.0+ smart phones with wife-approved easy encryption [OTR, OMEMO, or GPG].
Linphone is one of the most famous open source softphones in the world. It is fully SIP-based, for all calling, presence and IM features.
Does not allow connecting to sip server
Feature-rich XMPP client for advanced users offering strong customization options, secure encrypted messaging (TLS, OpenPGP, OTR, OMEMO), file transfers, audio/video calls, support for animated emoticons, modern themes, group messaging, and multi-platform compatibility.
LINE is transforming the way people communicate, closing the distance between family, friends, and loved ones for free.
Video conversations with up to 8 people in your browser - no downloads, no login. Just name your channel and you are on. Works in all modern browsers, even mobile.
MicroSIP is a free portable SIP softphone for Windows based on PJSIP stack. It allowing to do high quality VoIP calls (P2P or on regular telephones) via open SIP protocol. From cloud of SIP providers you can choose best for you, register account and use it with MicroSIP. You'.
Zoiper IAX & SIP multilanguage and multiplatform (Windows, Linux and Mac OS X) softphone is a VoIP soft client, meant to work with any IP-based communications systems and infrastructure.
All the same features, same look and feel changing skin. The only cons: Can't make conference or transfer unless you pay. Can't set up auto answer as well (available in licenced version)
It shows options to change the call configuration after the set up unlike others where we cannot change the account configurations.
Zoiper requires one of their selected providers, you can't add a local PABX.
The last version was released in June 2021.
Does not include SIP client softphone functionality.
FaceFlow is a free web-based application for video calling and group video calling. It also offers additional features such as chat rooms.
Canada
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Bulgaria
Does not allow connecting to sip server