Minecraft chains were introduced in Minecraft 1.16: The nether update - However in my opinion they are not quite complete... because Minecraft chains currently can't do what chains are made to do, PULL STUFF! Thankfully Gnembon (Member of the scicraft server and creator of the Minecraft carpet Mod) has introduced Minecraft chainstone into the 1.16.3 Carpet mod. It makes chains work like slimeblocks and honey blocks, but without things sticking to the sides. This is definitely one of the features I would like to see in Minecraft 1.17!