In their Media and Analyst presentation today Microsoft announced that Facebook Messenger is coming as a stand-alone app to Windows Phone.
On Android the app lets you use Facebook Messages without opening the full Facebook app and features:
Get to your messages without opening Facebook.
Chat with groups and make plans on the go.
Bring messages to life with stickers.
Send photos privately.
Keep the conversation going: with chat heads, you can chat while using other apps.
Text your phone contacts, even if you’re not Facebook friends.
Share your location so people know when you’re nearby.
Record voice messages.
Make free calls, even to friends in other countries.
Know when people have seen your messages.
See who’s available on Messenger and who’s active on Facebook.
Stay logged in so you never miss a message.
Turn off notifications when you’re working, sleeping or just need a break.
The app may presage the removal of Facebook Messaging from the built-in Messaging app in Windows Phone 8.1.