About Polymer
It's a set of libraries designed for creation of server side content, that work for player's without mods or (required) resource packs! You can create blocks, items and entities, that not only will work fully on server side (and singleplayer), but also are represented on server the same as normal (vanilla/modded) ones allowing for way better mod compatibility and way less weird edge-cases.
It is also should be fully compatible with close to all other mods and in case of found issues they are patched as soon as possible.
User guides
Mod development / Library usage
Polymer Core
eu.pb4:polymer-core
It's the heart of Polymer. It allows you to create server side content. It also contains lots of extra mod compatibility for client mods, to make your mod better fit for any modpack.
Polymer Resource Pack
eu.pb4:polymer-resource-pack
Allows creating global (and mod specific) resource packs. It also patches PolyMc to make it's resource generation work with polymer.
Polymer Networking
eu.pb4:polymer-networking
Polymer's Networking API. Uses its own custom synchronization code. Contains extra API, more specific that aren't available in fabric.
Polymer Virtual Entity
eu.pb4:polymer-virtual-entity
Allows you to create virtual/packet based entities in a quick and simple way, with support for attaching to any entity and chunks.
Polymer Blocks
eu.pb4:polymer-blocks
Extension of Polymer Core and Resource Pack. Allows creation of textured blocks.