Claims to be the most popular open source XMPP/Jabber client for Android. It uses Off-The-Record (OTR) for message encryption and is available in multiple languages.
Voice and video calling and group chats. No phone number or contacts sharing required. One of the few that allows group calls with up to 128 conversations all end-to-end encrypted. Sign up on the web
Messaging, voice, video, and group calls. File storage and sharing. Calls and messaging are peer-to-peer with no servers in the middle. Premium and business plans.