Monal is an open-source XMPP instant messaging client for iOS and macOS. It aims to be the go-to client on Apple platforms in the same way Conversations is on Android: federated addresses of the form user@domain, end-to-end encryption, and interoperability with other XMPP apps.
The client ships OMEMO encryption and audio/video calls, a reworked chat UI, and extended calling (including a dialpad for XMPP-VoIP bridges such as jmp.chat). Push for encrypted group chats uses standardised XMPP rather than a vendor-specific protocol.
Project page (NLnet): Monal, Monal UI / A/V.