If you’re in America and have Verizon as a carrier, Verizon Messages is one RCS alternative to Google Messages. RCS apps are marketed as “joyn” or “Message+” in other places as well, but most of them have been shutting down after about a decade of service because nobody but Google cared about RCS.

Until someone makes an RCS app for Android, you’ll have to use Google Messages for RCS functionality. Most messenger apps seem to be waiting for Google to add RCS to the SMS/MMS API rather than implement RCS themselves, though, so it’ll probably be a long wait.