I’m looking at adding similar features to an app.
They use Discourse, is a Rails base forum.
I use the wappalizer chrome extension to see all technologies that used on w/s )))
The ionic forum uses Discourse which is a discussion platform built using Ruby On Rails for the back-end and Ember for the front.
It is mobile-ready and has a responsive design so you can use it on your mobile. However, I am not sure if you can embed it into an App. If that what you want, you can always redirect to an external website where you have deployed your Discourse platform. For example, you can have a mobile application with a forum button that will redirect you to
Source: [The Discourse Github repository] (https://github.com/discourse/discourse)