Aroma1997Core is a library mod, and like other library mods, it includes a ton of code that is commonly used by many other mods, all of which are from the same author. Mod makers use these library mods as an anchor for their other mods, plugging redundant data into the library mods to cut down on file size for their other works, which are all programmed to rely on the library mod for specific bits of scripting. Because of this, library mods are often necessary for other mods to work, and Aroma1997Core is no different in this respect.
On its own, this mod doesn’t do very much. You can use /sleep to check who is sleeping on a server, as well as /sleep inform, which will tell the server where you’re playing that you want to sleep. Using /a sleep kick can force the issue by kicking all players not sleeping, allowing you to make the night progress into the day by hopping into bed yourself. If you’re looking for a list of affected mods, the author maintains a small wiki page for Aroma1997Core so that you can find a full list through that site. The odds are you won’t be needing this unless you use any of those.
It adds the “/sleep” command (That will tell you who’s not sleeping.)
It adds the “/sleep inform” command (That will inform everyone who’s not sleeping that you want to sleep.)
It adds the “/sleep kick” command (For operators, it’s possible to kick everyone who’s not sleeping.)
It adds a command-based Mail-System: “/mail send <target> <message>” and “/mail read”
This mod doesn’t have to be installed on the Server and Client. You can still join servers that have that mod installed with a client without that mod. You can also join a server that doesn’t have that mod installed with a client with that mod.
If your Minecraft says, Aroma1997core wasn’t loaded or is required for another mod, make sure you have the proper version for your Minecraft version.