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
The project is no longer actively developed, and is provided in hope it will be useful to others. For mature implementation of similar ideas, take a look at Delta. For a maintained implementation of a chat program in Gio, see Arbor.