Element / Matrix
Briar is an open-source software communication technology, intended to provide secure and resilient peer-to-peer communications with no centralized servers and minimal reliance on external infrastructure. Connections are made through Bluetooth, WiFi, or over the internet via Tor and all private communication is end-to-end encrypted. Relevant content is stored in encrypted form on participating devices. Long term plans for the project include "blogging, crisis mapping and collaborative document editing."
Session is an open-source, public-key-based secure messaging application which uses a set of decentralised storage servers and an onion routing protocol to send end-to-end encrypted messages with minimal exposure of user metadata. It does this while also providing common features of mainstream messaging applications.