Free and Cross Platform messaging and emailing app that combines common web applications into one.
Franz is a free messaging app / former Emperor of Austria and combines chat & messaging services into one application. Franz currently supports Slack, WhatsApp, WeChat, HipChat and many more. You can download Franz for Mac, Windows & Linux.
Ripcord is a desktop chat client for group-centric services like Slack and Discord. It provides a traditional compact desktop interface designed for power users. It's not built on top of web browser technology: it responds quickly to input, sips gently from computer...
WebCatalog lets you turn any web apps into desktop apps (a.k.a. site-specific browsers) with many additional features to enhance your workflows. It also protects you from cross-website trackers and preserving your privacy.
Empathy is a messaging program which supports text, voice, video chat, and file transfers over many different protocols. You can tell it about your accounts on all those services and do all your chatting within one application.Discontinued
Empathy is currently unmaintained. Last version, 3.25, released in August 2017, can be still downloaded from the official website.
Nertivia is an chat client that allows you to chat to anyone across the world. There are a lot of features that don't require you to pay at all such as, gif profile pictures, free custom emojis and more coming soon!
Shift is an email client that makes navigating between Mail, Calendar, Drive + your favorite Apps & Extensions easy (for Gmail, Outlook.com - Office 365 & Hotmail).
Kopete is an instant messenger supporting AIM, ICQ, Jabber, Gadu-Gadu, Novell GroupWise Messenger, and more. It is designed to be a flexible and extensible multi-protocol system suitable for personal and enterprise use.
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).