Purpur
A fork of Paper that adds a large set of extra gameplay and configuration options while staying compatible with Paper plugins.
Purpur is a server software built on top of Paper. Everything Paper does, Purpur does too, and plugins for Paper, Spigot and Bukkit run on it. What Purpur adds is configuration: a purpur.yml file with a very long list of toggles for gameplay mechanics that vanilla and Paper do not expose.
What kind of options
Purpur’s settings mostly change how the game plays rather than how fast it runs. Examples include making mobs rideable, adjusting individual mob behaviour, changing mechanics such as farmland trampling, and many quality-of-life tweaks that would otherwise need a plugin. The exact list changes between versions, so check the Purpur documentation for the version you run.
Why it matters for server owners
If you run a survival or SMP server and find yourself installing several small plugins just to change one mechanic each, Purpur can replace some of them with a config line. Fewer plugins means fewer things to update and fewer sources of errors.
The trade-off is that Purpur is a fork of a fork. New Minecraft versions reach Paper first, and Purpur follows once its own patches are updated. If you always want the newest version on day one, plain Paper is the safer choice.
Practical tip
Switching from Paper to Purpur is usually just swapping the server jar; your worlds, plugins and Paper configs stay in place. Take a backup anyway, start the server once to generate purpur.yml, then change only the options you actually need. Leaving the defaults untouched keeps behaviour close to Paper, which makes it easy to go back if you change your mind.