Jami

Free open source end-to-end encrypted peer-to-peer calling and messaging app. It supports video calls, audio, messaging and has a Skype-style interface. It has apps for all major platforms including Android, iPhone/iPad, Linux, Mac and Windows.

Fediverse address:
@Jami@mstdn.io

Delta Chat

Free open source end-to-end encrypted messaging system that works through email. This means if you both have Delta apps running you can chat in encrypted mode, but even people without Delta can chat with you through their normal email account. It’s available for Android, iOS, Linux, Mac and Windows.

Fediverse address:
@delta@chaos.social

Snikket

XMPP-based free open federated messenger project. It aims to make XMPP into a more viable alternative to Whatsapp etc by providing consistency in design and terminology, while still maintaining compatibility with other XMPP apps and servers. (It’s a similar plan to how Mastodon made ActivityPub more mainstream while still being compatible with other ActivityPub server types.)

Fediverse address:
@snikket_im@fosstodon.org

The XMPP Standards Foundation

Develops and maintains the XMPP standard for instant messaging and voice and video calls. It’s a free open federated standard, so anyone can set up their own server or write their own app. (XMPP used to be known as Jabber.)

Fediverse address:
@xmpp@fosstodon.org

JoinJabber

Informal collective promoting the use of XMPP/Jabber messaging. They run a non-technical website, also called JoinJabber, which helps people sign up on XMPP and includes advice on apps and servers.

Fediverse address:
@joinjabber@indieweb.social