why would the devteam clone their own app?
has to be a reason right? seems logical to me.
The darkMX home page seems to explain it rather well:
DarkMX is a new decentralized communication app that utilizes Tor hidden services to allow you to easily have an anonymous, reliable, and censorship-resistant presence on the internet.
...
You can create your own custom .onion site, available to anyone with a Tor Browser.
Incoming ports or UPNP mappings are not needed.
Firewall exceptions are not needed.
No .NET or Java dependencies.
...
