zzdec is merely an updated version of ZZT32's original zdec, a command-line tool for decompressing Zelda roms. New features include:

• Automatic detection of and support for byte-swapped and Little Endian Zelda roms. Additional reading on that can be found here.
• GUI version (zzdec-gui) for Windows users who don't understand the command line.
• Hopefully less complaints from antivirus software than zdec, but only time will tell.

Props to CDi-Fails for such thorough testing. Thanks, man!