While the latest Facebook app update brought Chat Heads for Messenger to iOS, they can only be used inside of the Facebook app, unlike on Android where they can float over apps system wide. Jailbreak developer Adam Bell is changing that with a tweak that will allow the Chat Heads feature to be used outside of the official FB app. Read more at The Verge.
Personally, I don't even use Facebook Messenger--but I'm glad to see the jailbreak community bringing the feature to iOS for those who do. Will you use it?