[derwiki]

I’ve been using Beeper to use Facebook messages without using Facebook directly.

[deergomoo]

It’s also worth noting that you can continue to use Messenger with a de-activated Facebook profile.

[astura]

Messenger is a different app, you can install it without having the Facebook app installed.

[dicknuckle]

I've been using Disa.im but every few years FB breaks the API it uses for a few days or weeks at a time.