Scatter implements the Signal protocol over federated email.
Very early version to be presented at my Gophercon 2019 talk about Gio.
Android Beta in the Play Store.
iOS Beta in TestFlight.
See the Gio guide for a setup guide for your platform. Then
$ GO111MODULE=on go run scatter.im/cmd/scatter
for Linux, macOS or Windows. For iOS and Android
$ go run gioui.org/cmd/gogio -target <android|ios> scatter.im/cmd/scatter