Scifer

Scifer is an archiver which claims to be best at compressing things with "complex, non-literal and precompressed information".

It is able to create archive files with the header information in a separate XML file (where the binary data is in a file with the .ba extension, and the XML header file has a .xml extension), or a combined archive file with headers with the .sen extension.

Format info

 * Documentation including info on file format

Other links

 * Official site (some of the links don't work, because they go to scifer-compression.com, which seems to have lapsed and now goes to a parking page with annoying 'sponsored' links)