What?: ThatPacketAddon - Skript Addon that lets you send packets to client. Requires ProtocolLib 4.4.0+.
Where?: https://forums.skunity.com/resources/thatpacketaddon.847/
Why?: Packets allow us to interact to directly interact with the minecraft protocol. This used to be on Minehut (not this specific addon, but sending packets). At some point, Minehut did not want outgoing HTTP requests or something, so they removed all of the addons that had that feature: that included MundoSK, since MundoSK had websocket client. Issue was that MundoSK also had the packet functionality, so that was a shame.
However, the same author made an addon (quite recently too), ThatPacketAddon, that is strictly for packets. So I do not see a reason for it not to be added unless the addon has other features I am unaware of.
Also, we can already LISTEN to incoming and outgoing packets, we just cannot send arbitrary packets to clients.