ALZ is an archiving format that is native to the ALZip archiver software, which also supports a number of other formats. One feature of the ALZ format that is promoted by the software makers is its ability to handle files of arbitrarily large size.
Newer ALZip versions have a new "native" archiving format, EGG.
ALZ files begin with bytes
'A' 'L' 'Z' 0x01.