Stackz was originally built for Japanese, where at least 3 attributes are used - Kanji (Japanese characters), Reading (the pronunciation of the Kanji, in Hiragana characters), and the translation of the entry, to any language. The 4th field was introduced for optional comments, it is not always used.
The attributes can be freely renamed to contain any kind of information, not just language related things. The number of attributes is always 4, no customization is supported at the moment. Unused fields are simply ignored and left blank when entering the data.
NOTE: The
skills (attribute appearance sequences) are in line with the attributes. If you rename the attributes (because you want to store different information) you'll probably want to adjust the skills accordingly (because you want to train different skills).
More is here:
http://www.stackz.com/KooHelp/Stackz/DataOrganization/Skills.htm