Through the many years of minecraft there's been multiple duplication glitches. In 1.7.2 and you can place 2 pistons side bye side to and active it with a fast redstone electrical current and it dupes the block placed between the blocks here is a video: http://www.youtube.com/watch?v=Gj6l1H8CrPI and in 1.8.1 comes this nether duplicating glitch if you're wondering about this here is also another video: http://www.youtube.com/watch?v=Aqh8h69GwHI This also worked in 1.9. In the 1.1+ in single player you can simply throw items on the ground save and exit come back in pick the items up then hit ALT=F4 then open Minecraft back up and go back in the world the items you picked up will be on the ground and in your inventory. But for multi-player in 1.1+ except 1.3+ there was a glitch was a glitch including the hacked client Nodus or any other client with freecam here is a video that explains it pretty well: http://www.youtube.com/watch?v=6HKAGP-X6vU And in some servers updated there bukkit servers to bypass this go here: http://www.youtube.com/watch?v=1GvoUv6ww2I For the new 1.3.1 update you could use a dispenser and have a redstone flashing current going on and off it would dupe the items only for bukkit version R0.1 which most servers don't run on anymore so to dupe now go to the latest link I posted Now for the other version of Minecraft like the XBox there are many ways to do it but here is a really good one: http://www.youtube.com/watch?v=U6gRHUl-_gY and in the pocket version for IOS devices or known as in a nutshell are the Iphone and Ipod and Ipad's There isn't one yet sadly cross your fingers and hope for it :D.

In alot of these dupes they invole of getting a block with a value of -1 if there is a way that we can do this in the newest update please post in the comments add a link or something I hope you enjoyed