Methods to create infinite items are taken as duplication glitches. More information can be found on the Infinite Items article. Server Exploits - Duplication Exploits
During the lifespan of the server, a number of duplication exploits have been abused. [THE LIST MAY BE INCOMPLETE! PLEASE SUBMIT OTHER DUPLICATION METHODS]
Methods to create infinite items are taken as duplication glitches. More information can be found on the Infinite Items article.
1) Client sided inventories:
During the Alpha era, inventories were client sided. Because of this, they could be easily edited using Cheat Engine.
2) Infinite items:
During Beta - Release 1.0, you could create Infinite items. More information on the Infinite Items page.
3) Minecart dupe:
The most popular dupe in 1.4.7 was the Minecart dupe. This was because it was easy to setup and do.
4) Minecart dupe (BOAT BYPASS):
While the normal minecart dupe got patched in 1.5, you could simply go into a boat and it would start working again.
5) Minecart dupe (NO FREECAM METHOD)
I am unsure as to when this dupe was used, but you could still do the minecart dupe by simply taking the items out quickly. You could only do this with 1 slot at a time, but it would still work.
6) Donkey dupe:
In 1.7.10, the donkey dupe was active. Combined with NCP being turned off, you could easily find donkeys by flying around until you find new chunks.
Currently there are no active dupes.