If you're interested in developing server side Fabric mods, check out the Fabric Server-side Development discord, and ping me (comp500#7396) if you find a server side Fabric mod not listed here.
Also see Optifine alternatives on Fabric for a few useful client side only mods!
Mods on this list are marked as outdated when they are two major Minecraft versions old - e.g. if 1.16 is the latest version, 1.14 and older mods are considered outdated.