Caliopen is described as 'All of your private messages (Email, Facebook, Twitter, Instagram etc.) through a single login. A single timeline, a unified contact list and simplified searches to manage all your private messages. Unified message management' and is an website in the Social & Communications category. There are more than 50 alternatives to Caliopen, not only websites but also apps for a variety of platforms, including Mac, Windows, Linux and Android. The best alternative is Rambox, which is both free and Open Source. Other great sites and apps similar to Caliopen are Ferdi (Free, Open Source), Franz (Freemium, Open Source), WebCatalog (Freemium, Open Source) and Ripcord (Free Personal).
VideoMeeting is a free and open source video conference solution built to have video calls and chats using your web browser. It is a pure web application based on WebRTC that can provide communication features within your web browser.
Daily is an audio and video API. Easily build video chats in your web or mobile apps with an API built on top of WebRTC or drop in the Prebuilt UI for fast video conferencing integration. 1,000 person video and audio calls. HIPAA compliant.
Fully open source instant messaging server and clients. No proprietary components or non-free dependencies. Backend in pure Go (GPL 3.0), with a command-line administration tool in python + gRPC. Clients for Android, iPhone, and Web - ReactJS (all licensed under Apache 2.0).
Group messaging platform owned by Microsoft. It's absolutely free, whether you're talking to a group of friends, or texting with one person. Best of all, it works on nearly every phone, via push or SMS. With GroupMe, it's easy to reach anyone, anytime, anywhere.
Stack is a Reinvented internet launchpad, increasing the efficiency of working with the web by allowing simultaneous use of multiple apps within a neatly organized working environment & immersive split screen view.
Skype Lite lets you send free text messages and make voice & video calls even under limited network conditions. Stay connected Skype Lite is optimized for 2G and unstable network connections, so you can stay connected with friends and family.