The Legend of Zelda: A Link to the Past
Legend of Zelda:A Link to the Past has been extensively hacked.
Hyrule Magic is the principal Legend of Zelda: A Link to the Past editor. It is available here.
SadNES City translated this game into Italian. You can download it here.
There is a very thorough Zelda 3 hack currently being developed by GameMakr24 called Zelda 3 Challenge: Quest for Calatia. When completed, this will be an entirely different game in the Zelda series, featuring new worlds, music, graphics, and dialog. Information on this hack is available here.
GameMakr24's site is down, and has been down for some time. Hopefully his Zelda hack is not dead, as it looked really cool. If anyone has any info about the current status of Zelda: Quest for Calatia, they should post it here. GameMakr24's hack from Zelda 1 on the N.E.S. was the best, so hopefully this hack is still in the works.
According to a post by GameMakr24 on ACMLM the project is still going on.
GameMakr24 was previously responsible for the Zelda Challenge: Outlands, which did a similar feat for Zelda 1 and had over 130,000 downloads.