Google Messages / Messages for Web uses QR codes so you can send and receive messages from your web browser:
https://messages.android.com/
The process is simple but is explained in more detail here:
https://support.google.com/messages/answer/7611075
I’ve found this use to be particularly helpful checking messages when my phone is elsewhere (if I enabled it beforehand) and when sending messages to groups when I have lists that aren’t on my phone.