Aternos - With Aternos, you can run your own Minecraft server for free.
PaperMC - Paper is a fork of the Spigot server implementation (which is itself a fork of CraftBukkit). Paper strives to bring improved performance, more features, and more APIs for developers to build awesome plugins with.
Spigot - Simply put, Spigot is it.
PloudOS - Why buy a server if you can get one for free? Get your own Minecraft Server for free today!
Server.pro - Free and premium game servers for Minecraft, Terraria and Hytale
Glowstone - A fast, customizable and compatible open source Minecraft server.