Bukkit

Spawn zombie/skeleton horses.

Gives users a spy network for information about other players

HulkSmash

Stops players from digging under their feet in a painful manner.

Prevents people from using fullbright hacking, or atleast slows them down

Modify items to your will!

Changes enchant costs from levels to XP.

Players can't modify items' slots.

DaylightSensorExpanded

Allows addition of potion effects to items as enchants, as well as adding commands to change item names and enchant them

TimerSigns

HealthPerKill

Get drunk.

ShopsNRobbers lets you easily set up Raidable Shops and Heistable Banks

Freeze the ground, players, mobs and moving things like arrows

Opening a chest has a chance for a bat to spawn.

Gives players a random block or item on an interval.

Aappartment

Sets a player's max health based on their xp level

Fells, or chops down, trees automatically, similar to the Timber mod.