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There's also a lite version of Facebook for those who want Messenger without an app.

Also https://www.messenger.com/ for Facebook Messenger without the app or the Facebook.

If you have 'mobile' or 'tablet' in your useragent this URL only offers a link to download the app.

However, for desktop it's great - I use it (and web.whatsapp.com) with Chromes --app= parameter to emulate the app experience.