The user-friendly, lightweight, and fast email client

DavMail POP/IMAP/SMTP/Caldav/Carddav/LDAP Exchange and Office 365 Gateway.

eM Client is a full featured e-mail client with a modern and easy to use interface. eM Client also offers calendar, tasks, contacts and chat.

Mailspring for Windows

A free email client from Mozilla

Postbox mail client

IMAP & SMTP bridge for ProtonMail.

HexChat is an IRC client based on XChat, but unlike XChat it’s completely free for both Windows and Unix-like systems.

HydraIRC is an open-source IRC client with an attractive and easy to use interface.

KVIrc is a free portable IRC client based on the excellent Qt GUI toolkit.

mIRC is a popular Internet Relay Chat client used by millions of people, and thousands of organizations, to communicate, share, play and work with each other on IRC networks around the world

Quassel IRC is a modern, cross-platform, distributed IRC client based on the Qt4 framework.

P2P communications protocol used to send encrypted messages to another person or to many subscribers

An elegant, privacy-focused Facebook Messenger app

Confide lets you take your messages off the record.

CoyIM is a new chat client that is safe and secure by default: no settings to change, no plugins to install, no computer configuration to change.

Cryptocat - Chat with your friends, securely.

Digsby - IM, Email, and Social Networks in one easy to use application!

Franz is a free messaging app / former Emperor of Austria and combines chat & messaging services into one application.

>Full featured and easy to use Jabber/XMPP client

Gitter. Where communities thrive.

Whether in a 1:1 chat or a dedicated group workspace, Hangouts Chat makes it easy to collaborate with your team in an organized way. Share and discuss Docs, Sheets, and Slides all in one place.

HipChat is group chat, file sharing, video chat & screen sharing built for teams & business.

Multi-protocols instant messaging application

Keybase is a free, open source security app.

Free SMS, Free Voice call messenger application.

Miranda IM is a multi-protocol instant messaging client for Windows.

Miranda NG is a multi-protocol instant messaging client for Windows

Pidgin is a chat program which lets you log in to accounts on multiple chat networks simultaneously.

Instant messaging application for the XMPP network

Development branch of Psi IM XMPP/Jabber client.

Pushbullet for Windows.

Free, Open Source and Cross Platform messaging and emailing app that combines common web applications into one. ALL WILL BE DIFFERENT...

RetroShare is a Free and Open Source cross-platform, Friend-2-Friend and secure decentralised communication platform.

Fast, simple, secure. Privacy that fits in your pocket

Skype - VOIP

Slack for Windows

Cloud-based synchronized messaging app with a focus on speed and security

TIM —— Tencent Instant Messaging

Proprietary multiprotocol instant messaging application

Wassapp is an unofficial desktop client for WhatsApp, the popular mobile application to send and receive free instant messages.

WhatsApp Messenger is a cross-platform mobile messaging app which allows you to exchange messages without having to pay for SMS

Open, free and uncensorable websites, using Bitcoin cryptography and BitTorrent network

tweetdeck

Gadget-like Windows Desktop Twitter Client

Discord is an all-in-one voice and text chat for gamers that’s free, secure, and works on both your desktop and phone.

Discord Canary is Discord's alpha build

Open source SoftPhone (VoIP), Video Conferencing and Instant Messenger

Voice Communication

Jitsi is an audio/video and chat communicator with many useful features.

Open source portable SIP softphone for Windows based on PJSIP stack

Mumble is an open source, low-latency, high quality voice chat software primarily intended for use while gaming.

Easy to use VoIP softphone with profile and contact management

TeamSpeak Client

Make free phone calls and send text messages

VoIP Client for IP Telephony.