Conversations is an Android client for the federated network of instant messaging servers that use the Extensible Messaging and Presence Protocol (XMPP). It aims to provide a feature set and user experience on par with well-known proprietary messengers while keeping federation and open standards.
The app supports end-to-end encrypted text messages, images, short videos, and voice messages, plus audio and video calls via standard Jingle extensions so Conversations interoperates with other XMPP clients rather than forcing a new silo.
Project page (NLnet): Conversations.