TWiM is a new (free) iPhone app that turns Twitter direct messages into an instant messaging service.
It comes with an iMessage-like interface, support for rich links, interactive notifications, 3D Touch and even SiriKit. Simply say “Send a message to Craig with TwIM,” and Siri will ask what you want to tell Craig about your busted-ass Mac Pro.
I don’t know about other people, but I rarely use Twitter DMs. iMessage and Slack are how I communicate with most people, but TWiM is so well done, I’m keeping it around and have turned off DM notifications in Tweetbot.