The Salmon Library Minecraft Server has a number of tweaks and datapacks that alter gameplay. This is a list of all of them in effect. There are a few custom crafting recipes. See the following box for more information about those.
You can read information about VanillaTweaks datapacks on the linked website, or through the Advancement menu in-game (default hotkey: "L").
You can read about the following through the in-game recipe list, or through the Crafting Tweaks page on the Vanilla Tweaks website.
There are a few custom crafting recipes that are accessible through this server: saddles, nametags, dragon egg to shulker shells, rotten flesh to rabbit hide, and poison potato to gunpowder. That last one is just to give the stupid poison potatoes something to do.