osu! has a tournament client (called ‘osu!tourney‘) that essentially spectates all players in the multiplayer lobby at once. There is an official wiki page for it here…
How to set it up?
There are a lot of caveats (slots, which ones correlate to which square, etc).
- https://osu.ppy.sh/help/wiki/osu!tourney/Multiplayer_Usage/
- https://osu.ppy.sh/help/wiki/osu!tourney/Spectator_Usage/
What about a skin for the tournament client?
- Read more here: https://osu.ppy.sh/help/wiki/osu!tourney/Skinning/