i need Plugin info

So I was looking at a server list and I noticed one of them had a <servername> core.phar plugin. What is this and how do you get one?

They are custom plugins and they obviously have a own name

Oh I see, so would people make a custom plugin for free or money?

What kind?

People make their own custom plugins just for their own servers, like i do. It is free to do, yet time consuming.

You can learn to make your own plugins, or ask some people who know how to to make for you. Whether it takes money depends on how well you know him, whether he is wiling to, etc. Plugin development itself has no cost other than electricity bills and time. It is just like asking to be done a favor.