Previously if you had to use Facebook Messenger, you had to login to Facebook on desktop browser, but now a standalone service called Messenger is available.
You can simply login with your Facebook account and you will see all the conversations loaded. Similar to the version available on Facebook.com, the Messenger website also allows you to make calls (voice and video) from the browser. You can make free HD calls from Facebook using this service, you will be charged only for Wi-Fi or 3G connected. You can also share photos using the service and add stickers to your conversations.
As of now Messenger is still available on Facebook.com unlike the company’s move to separate both apps on mobile platforms. In future, we could even see Messenger growing out as an independent platform for social networking.