I don't know why SilenceIM isn't more popular. It's a fork of Signal's now-discontinued SMS encryption. Usernames are still telephone numbers (because SMS) and metadata is still leaked (to telcos, because SMS) but there's no reliance on any centralised servers or organisations, no requirement for Play services, and delivery is as reliable as regular SMS.

I don't know the real reason for Signal getting rid of SMS encryption but it's the only feature I'm interested in. I can get glorified internet messaging anywhere, but OTR encryption over SMS is a difficult problem due to the inability to conduct handshakes. We should not throw this work away.