Format .sxw was created for program StarOffice Writer, later on it was revised for OpenOffice.org Writer. Basically he is very similar to .odt file format, which is now used as its substitute. Essentially it was used in first versions of OpenOffice.org, after that .odt file format was released and used, but .sxw file format is still supported by OpenOffice.org Writer.
It was developed by Sun Microsystems Inc., which was later bought by Oracle (company developing great databases and owns programming language Java).
Its main advantage is similarity with .docx file type. Notwithstanding .sxw is quite old file format, it was created 15 years ago, it handles very well long texts, simple graphics, text formatting, font stylization and coloring of text. He can also create graphs.
Conversion between .sxw and .odt can be achieved very simply. OpenOffice himself is supporting this conversion.