Ring (SFLphone) is an open-source SIP-compatible softphone and instant messenger for Linux, Microsoft Windows, OS X and Android. Developed by Savoir-faire Linux
License: Open Source
CSipSimple is an open-source SIP client that offers extensive customization and codec support but may be challenging for beginners. In contrast, Ring prioritizes user-friendliness and security, making it suitable for users who value ease of use and privacy.