There are 4 repositories under spigot-fork topic.
A Server Platform for Minecraft: Java Edition based on Paper which provides many optimizations and features
EmpireCraft Server Software
Exploring the deepest depths of forking
Patch for PaperSpigot with many features.
High performance PaperSpigot fork used by Minecraft Server Cloudz.ml.
All your plugin needs...
High performance Spigot fork that aims to fix gameplay and mechanics inconsistencies
this is very broken and dead, dont use it. a fork of purpur with more stuff
Example fork of Ilblu, adds upon the event api
Server platform with features too experimental to implement into Plazma
Paper 기반의 여러 개선이 추가된 Minecraft: Java Edition 용 서버 플랫폼 | A Server Platform for Minecraft: Java Edition with many improvements based on Paper