Thanks. Yes, it's as the nick suggests - I'm the author of GS-Base.
Re: the default file format, this is a native/private ("partially binary") file format. Nevertheless it should be quite safe as all the data is stored in the zip file in its original format. That is, tables with records as plain utf-8 text files, memo files as *.txt or *.rtf files etc.
To clarify this better I just uploaded a page from the help file:http://www.citadel5.com/help/gsbase/file_format.htm
(Just one page at this time.)
The supported file formats are listed on the homepage: dBase, Clipper, FoxPro, text, XML, Excel XML, HTML, PDF. (XML, PDF - export only.)
The coupon is valid for GS-Base licenses only.