SQX is an open-source archive format developed by Sven Ritter, Rainer Nausedat, and SpeedProject. It seems to have been created as part of the development of its primary implementation, a program called "Squeez", which originated in 1993 as a utility for manipulating common archive formats, with no format of its own. (See Squeeze for a list of formats with similar names.)
The source code download includes a text file giving file format details. The source code is archived as a .sqx file itself, but fortunately an SQX extractor is also included as a standalone Windows .exe. (Bad luck for users of any non-Windows platform, though.)
-sqx-" appears at offset 7. Though this is reminiscent of LHA compression identifiers, SQX is not closely related to LHA.
- Wikipedia article
- Official site (from archive.org)
- Total SQX plugin for Total Commander file manager
- Some discussion of SQX