Bukkit

Version 1.9

• Changed the way commands work.
  
• Fixed spectating players not being able to shoot projectiles and not being hit by projectiles.
  
• Added a '/spectate inv' argument that toggles inventory on and off.
  
• Added a spectate scan mode that switches through players at an interval. Type '/spectate scan (interval in seconds)' to enter the scan mode.
  
• Made players not able to interact with doors, levers, buttons, etc... again. This was accidentally removed in the previous version.
  

Version 1.8

• Added a new spectate mode which lets you scroll through players! Typing in /spectatemode (1/default|2/scroll) will change your spectate mode.
  
• Right clicking and left clicking while in the scroll mode will scroll through players.
  
• You can now see the contents inside of a chest, dispenser, or furnace when the player you're spectating opens one.
  
• Fixed players that are spectating being able to take items out of chests.
  
• Fixed mobs targeting players that are spectating.
  
• Possibly fixed interference with plugins that set different inventories per world. - This was untested, please tell me if it's still broken.
  
• Fixed players being able to enter minecarts while spectating.
  
• Fixed players being set on fire if they stop spectating while the person they were spectating was in fire or lava.
  

Version 1.7.1

• Fixed being able to start spectating the person you're currently spectating.
  
• Fixed EntityRegainHealthEvent thinking every mob was a player.
  

Version 1.7

• Made it so more than one person can spectate someone at a time.
  
• Made spectating a lot smoother, now you can see every little twitch they make.
  
• Removed the "Permissions enabled?" option in the config.
  
• Added a "canspectate Permission Enabled?" option in the config. Setting it to false will make it not check if someone has the "spectate.cantspectate" permission before spectating.
  
• Fixed being able to take damage while spectating.
  
• Fixed being able to inflict damage to players and mobs while spectating.
  
• Made it so people that are spectating can't interact with doors, levers, buttons, etc...
  

Version 1.6

• Added a spectate.cantspectate permission that makes it so the person that has it can't be spectated.
  
• Added /spec and /specoff.
  
• Made it so that doing /spectate (player) while spectating someone will make you start spectating that player, instead of having to do /spectateoff first.
  

Version 1.5.2

• Fixed still spectating a player after logging off.
  

Version 1.5.1

• Fixed being invisible after using /spectateoff.
  

Version 1.5

• Hopefully fixed hacked clients being able to see you.
  
• Using the new Vanish api.
  
• If you're spectating someone, you can now see their health and hunger
  

Version 1.4.2

• You will now get your inventory and armor back if you were forced to stop spectating.
  

Version 1.4.1

• If the server reloads while spectating, you will be sent back to your previous location.
  
• Minor bug fixes.
  

Version 1.4

• Disconnecting while spectating will now return you back to your original location.
  
• If the person who you are spectating dies or disconnects from the server, you will return back to your original location.
  

Version 1.3.1

• Fixed a bug that wouldn't let you spectate if you weren't op, even if you had the permission node.
  
• Added Herobrine. ;)
  

Version 1.3

• Added the ability to see their inventory and armor.
  
• Minor tweaks and bug fixes.
  

Version 1.2

• Added config for turning permissions on and off.
  

Version 1.1

• Stopped players from picking up items, dropping items, breaking blocks and placing blocks while spectating.
  

Version 1.0.1

• Fixed not letting you out of spectate mode.
  

Version 1.0

• First release