[MK2k]

First of all, I don't use any arr. From what I see the arr tools are used for obtaining media, less so presenting and providing a UI. Correct me if I'm wrong, but I assume that *arr tools and Media Hoarder might actually go well together.

[RockRobotRock]

Each project is separated in terms of the type of media they're used for (ex. Sonarr for TV, Radarr for Movies), but they share a common design language. They don't obtain media directly, but are commonly paired with Usenet/BitTorrent to obtain media. Aside from that, they allow similar functionality in terms of a pretty UI to organize and manage your collection. They have no playback functionality, though.

You should definitely look into them more because there's a huge overlap. Focus on what can set your project apart.