Simphone is described as 'Secure and private open source peer-to-peer Instant Messenger' and is a Encrypted Chat App in the Social & Communications category. There are more than 50 alternatives to Simphone for a variety of platforms, including Linux, Windows, Android, Mac and iPhone. Most alternatives are Encrypted Chat Apps and Instant Messengers. The best alternative is Telegram, which is free. Other great apps like Simphone are Signal (Free, Open Source), Element (Freemium, Open Source), Discord (Freemium) and Jitsi (Free, Open Source).
Signal is a messaging app with an unexpected focus on privacy, combined with all the features expected from a modern IM app. Signal has received a lot of praise from all around the world for its security and privacy-respecting technologies.
Element is a secure collaboration and messaging app based on the Matrix protocol. It’s decentralised to deliver digital sovereignty, and based on an open standard for easy connections and interoperability. It is end-to-end encrypted by default.
Whether you’re part of a school club, a gaming group, a worldwide art community, or just a handful of friends that want to spend time together, Discord makes it easy to talk every day and hang out more often. Create an invite-only place.
Jitsi (previously SIP Communicator) is an audio/video and chat communicator with full encryption that supports protocols such as SIP, XMPP/Jabber, ICQ/AIM, Windows Live, Yahoo!, GTalk/Hangouts extensions, as well as OTR, ZRTP, etc.
Wire is the most secure collaboration platform featuring messenger, voice, video, conference calls, file-sharing, and external collaboration –all protected by the most secure end-to-end-encryption. Why Wire?
Pidgin is an easy to use, multi-protocol chat client client used by millions. Connect to AIM, MSN, Yahoo, XMPP, and more chat networks all at once. It has built-in support for NSS, offering client-to-server message encryption for protocols that support it.
Jami (formerly GNU Ring, SFLphone) positions itself as a potential free Skype replacement Open Source and cross-platform. Jami gives you a full control over your communications and an unmatched level of privacy.
Mumble was the first and is the most successful and wide spread free and open source software for VoIP. It was the first VoIP software to provide low-latency audio suitable for gaming, and at the same time was a pioneer in high audio quality at the same time.