Access on web and mobile
Beautiful mobile commenting, on the web, iOS, and Windows.
https://disqus.com/features/
Disqus is a comment system imbedded into web pages.
I am not sure what an app would be used for that a standard web browser does not do.
The trick would be getting the app to know what site and page the comments are being posted on.Native app is much easier/fluid to use and you get reliable alerts.