Many times in the past people asked for tips, concepts or whatever to enhance the vanilla experience without using bukkit/spigot or external frameworks. Reading these threads I made a short (really) list of what would be nice having in my server:

• XP Bank – Saves XP as points in a scoreboard
• Death Counter – This.
• XP Fountain – Flows XP Orbs under random circumstances (just a concept)
• Skeleton Swords – Make skeletons switch to swords if a player is too close
• Place a grave at a player position upon death (I have to develop this concept)
• Custom Trees – Set custom tress on ground when you drop specific named items
• Contests – Classic minigames with random prizes at the end
• Easter Eggs – Secret events under particular circumstances (effect boosts, random items or chests, xp levels)
• SpawnPad – Set magic slab on ground when you drop specific named items
• PrisonDungeon – When little rules are broken the player is tped in a prison dungeon and he has to excape (increased difficulty, parkours, stronger mobs, a giant..)

What else? I'm trying making a list for a future vanilla server and I really need a lot of ideas to make the experience dynamic and fresh! What would you like to see in a vanilla server with no plugins?