Here there is the link: https://pastebin.com/FskYr6z1
I don't understand if the mod is clientside only or it can be used for multiplayer too

The mod is clientside only. It can be used in multiplayer, but it doesn't need to be installed on the server.

Not sure what you mean. All you need to do is install it on your client then connect to a server. The notes are stored purely on the clientside.

Yeah but, how can I use it in multiplayer?

Any chance you can make a version which stores the note-files on the server side? so that it can be used on private servers with friends having all access to the same note-files?