Matrix.org/riot.im has working federation, end-to-end cryptography, works without Google Play and is completely open source.
The encryption is audited, but not yet enabled by default, as there are still some rough edges. But the apps have tremendously improved over the last few weeks alone and I am very happy with it.
The encryption is audited, but not yet enabled by default, as there are still some rough edges. But the apps have tremendously improved over the last few weeks alone and I am very happy with it.