The 3.31-alpha-4 release of HTTrack introduces a new cache 
format, more extensible and efficient than the previous one 
(ndx/dat format). The main advantages of this cache are: 

- One single file for a complete website cache archive 
- Standard ZIP format, that can be easily reused on most 
platforms and languages 
- Compressed data with the efficient and opened zlib format 

This feature is still highly experimental, so expect bugs :)

Note: Of course, previous cache formats (dat/ndx) will 
still be imported by the new releases of httrack