Both QKSMS and Silence have been abandoned so open source apps are out of the question.
chromaggus messenger. You have to pay $3 but it is definitely worth every penny
Signal functions well enough for SMS. Or switch your friends to https://riot.im and enjoy your federated freedoms.
Textra.
>>62126594
Signal needs to be connected to their servers though.
>>62126480
just use whatsapp idiot -_-
>>62127580
europoor spotted