Scribus

Scribus is an open source desktop publishing application. It has a native Scribus Document format (SLA; SCD in older versions), among other native formats. It also supports many other DTP formats, vector graphics formats, and similar formats.

SLA format is based on XML.

Supported formats
Scribus 1.5.1[2015-12-20] claims to read the following formats:
 * Scribus Document
 * Windows Metafile
 * Uniconvertor Import
 * Scalable Vector Graphics
 * OpenOffice.org 1.x Draw (.sxd)
 * Microsoft XPS
 * Open XML Paper
 * Xfig
 * XARA
 * WordPerfect Graphics
 * Visio
 * VIVA Designer XML
 * SVM (StarView MetaFile) (.svm)
 * Kivio Stencils (.sml)
 * Dia Shapes (.shape)
 * Microsoft Publisher
 * PageMaker
 * PDF
 * Encapsulated PostScript
 * PostScript
 * Macintosh Pict
 * iWorks Pages (.pages)
 * ODF Drawing
 * ODF Presentation
 * Adobe Indesign IDML (.idml)
 * Adobe Indesign IDMS (.idms)
 * FreeHand
 * Enhanced Metafile
 * Micrografx Draw (.drw)
 * Calamus Vector Graphic
 * Computer Graphics Metafile
 * CorelDRAW
 * Adobe Illustrator

Specifications

 * File Format Specification for Scribus 1.4

Links

 * Scribus website
 * Scribus wiki
 * List of Scribus file formats
 * Scribus
 * XML Processing of SLA Files