Messenger from Google is a standalone app to send SMS and MMS to any phone. Oddly, it's not a direct replacement for Hangouts, as it doesn't support internet messaging or VOIP.

Messenger comes installed as standard on devices running Android 5.0 Lollipop and above. But any user can install it through Google Play if they have a device with Android 4.1 and above. But is it worth bothering with?