The (Actual) Last Release
It's been over 10 years since I first made this plugin, and man has it been special to look back on it. It's still actively hosted and joinable (using MC 1.12.2) at f13mc.com as part of the PilzBros Network. I've had to make some changes to the plugin's dependencies to get it to run nicely on Paper and in my new setup, so I'm sharing those files here.
This Release
This release is the same as 1.9, but includes a few extra things. Firstly, the release contains a bunch of JARs. It contains Friday the 13th plus every dependency F13 needs to run on 1.12.2, the last version of Minecraft it supports. These are everything you need to run your own F13 server.
The included SideBarApi (whose project is called ScoreboardAPI) JAR is a custom one. The fork can be found here. I had to remove a badly behaving dependency (PlaceholderAPI) within it to enable it to function with Paper 1.12.2. It's functionally identical otherwise.
ViaVersion Warning
This plugin does not support ViaVersion or any forwards/backwards dependency plugins. It uses NMS to force the skin changes via packet modifications. If a client does not have 1.12.2, the packet send fails. You'll get console spam when the game attempts to transition you from the waiting room and your console log will be spammed.