HDSlot2.1.1 is a release file of the Minecraft plugin Happydiggers Extra Slots [Let people log in even if the server is full!]. It was published on June 1, 2014 and is 0 MB in size. For the full description, screenshots and every other version, visit the Happydiggers Extra Slots [Let people log in even if the server is full!] plugin page.
How to install: Put the .jar into the plugins folder of your Paper, Spigot or Bukkit server and restart the server.