macOS and other non-Windows machines
  sudo ./rssfs

Why are you using sudo here? FUSE filesystems shouldn't require special privileges unless they're accessing privileged stuff like block devices owned by root.

(This is my first try to play with FUSE. I hope it's still OK.)

Windows support will follow later this year. Maybe. I’d really prefer to have two not-too-diverging code bases here. Need to experiment a bit...

I started to think there is a wheel-of-fuse somewhere and people are rolling it to match random things to build as FS.

What's the benefit of offering this via FUSE rather than having a program just fetch the same material and store it in the usual filesystem with the same folder and filenames? I assume there is one and I'm missing it. (Alternatively if this is for learning/experimenting, that's OK! :-))