No list as fair as I know.
Apart from subscription and the official app repositories:
# Default repository:
https://distfeed.nethserver.org/ns8/updates/
# Default "Emergency" repository (in case the default one above isn't working):
https://raw.githubusercontent.com/NethServer/ns8-repomd/repomd/
…there are some third-party apps repositories like:
# ----------------------
# 3rd-party Repositories
# ----------------------
# Nethforge repository:
https://forge.nethserver.org/ns8/updates/
# MrMarkuz repository (by @mrmarkuz) | WIP:
https://repo.mrmarkuz.com/ns8/updates/
https://raw.githubusercontent.com/mrmarkuz/ns8-mrmarkuz/repomd/ns8/updates/ # Emergency
# Genius Forge (by @oneitonitram) | WIP:
https://forge.genius.ke/ns8/updates/
Don’t know if @stephdl has its own repo or pushes directly to nethforge once done.
@mrmarkuz is working on some modules (maybe also its own repository or push to nethforge), if time allows him.