Prune by TreeOfSelf

Warning: Prune deletes chunks in your world file, so keep backups of your world and use at your own risk.

Prune

Description

Every server start, Prune deletes the chunks nobody actually used: the ones players only flew past. Bases, builds and anything players touched stay.

Much smaller world files. On Hardcore Anarchy, exploring adds 1-4 GB a day. Each restart takes the overworld back to ~5.5 GB and the nether to ~1 GB (one day: 11.3 GB down to 6.5 GB).
No chunk trails. Chunks loaded while someone travelled are deleted, so nobody can follow old trails to a base.
Fresh terrain for new versions. Deleted chunks generate again with the current version's terrain, so a world updated over many versions gets new caves, biomes and structures wherever nobody built.
No cut trees or cliffs at the borders. Trees and ores that crossed into a deleted chunk are put back when it regenerates, and new terrain lines up with old chunks instead of warping toward them.

What counts as used: placing, breaking or using blocks, dying, logging off, getting off a mount, dropped items, explosions, fire, pistons, portals, villager trades, named/leashed/tamed/ridden mobs, or 5+ minutes of players nearby.
Chunks from before the install are never deleted. What players did there before Prune was installed was never tracked, so on the first start every existing chunk is recorded and left alone. Only chunks made after the install are pruned ("pruneOldChunks": true changes that).
Safe to remove. Prune keeps its data in its own chunk flag and never edits vanilla data. Vanilla, Forge or a server without Prune just ignore it. Server-side only, nothing needed on the client.
No MCASelector or external tools: it runs by itself before the worlds load.

config/PandaPrune.json. Pruning is off until you set "pruneOnStartup": true.

pruneMinInhabitedTicks: time players must spend near a chunk to keep it without any interaction (6000 = 5 minutes)
pruneDimensions: empty = all dimensions
pruneOldChunks: also prune chunks from before the install (default false)
restoreFeatures, blendMode ("difference", "vanilla"), chunkBlending

hardcoreanarchy.gay (Deathban Anarchy)
sky.hardcoreanarchy.gay (Skyblock Anarchy)

No Lag - Stop common causes of lag on your server. Configure to your likings.
Occlusion - Server-side anti-freecam. Prevents players from seeing caves, ores and entities they can't see.
TNT Fusion - Stop massive amounts of TNT from lagging or crashing your server
Anti-Exploit - A drop-in mod for preventing common exploits. Fully configurable and works well alongside other anti-cheats like GrimAC.