Does Discord has an application that can be run on a Raspberry PI ? Their clients include mac/windows/linux (x86) or android, but I don't see anything for a system with ARM CPU.

As far as I know, RetroArch on PC/Mac/Linux has the possibility to interact with Discord, but in the end it needs to be properly integrated into RetroPie.

What are you thinking when you say 'integrating' ?
If it's already included in RetroArch, the you can configure it and you're good to go.

@pjft Would it be possible to write a batch script or something that could be run once to simply and easily categorize large quantities of roms without duplication?

My idea is something that works like this. It 'feels' like it would be easy for someone who does these sorts of things, but I know nothing so I could be very wrong.

in '/roms/nes' you make the directory 'Top 50' (or subcategorize by genre, etc.)
You move your top 50 roms from '/roms/nes' to /roms/nes/Top 50'
You put the 'categorize_roms.bat' into '/roms/nes/Top 50' and run it

The .bat file would then take all the roms in the folder, move them back up to '/roms/nes' and replace them with symlinks to each rom in the subfolder.

Obviously replace .bat with whatever kind of script you prefer - I'm working with limited knowledge here.

Is this doable?