Does anyone know of an open-source alternative to Google's "Messages" app, which takes care of SMS/text messages on my phone?

I was looking for open-source alternatives on PlayStore and F-Droid but can't really find anything – most apps seem to target some extra purpose than simply handling SMSs.

(Edit: I'd like to stay away from the "Simple Mobile Tools" line because I don't know if it's open source, and I don't like the way they promoted some apps – forcing users to update to pro and similar.)

Cheers!