Scribus is a free Open Source application that functions very much like Adobe Indesign. Both are used for Desktop Publishing (page layout design for newspapers, brochures, newsletters, posters, books, and pdf). Scribus can also create animated and interactive PDF presentations and forms.
Scribus is a page layout program that can be installed on Windows, Mac, and Linux operating systems. When saving and editing a file in Indesign, you won’t lose data by the inherent “trimming” function. What this means is that if you resize an image to 1/10th of its size the application gets rid of some data because you’re not using it. This function processed multiple times is what allows some documents (pdfs) to take up less space.
Scribus doesn’t have this function, so your files may be large depending on the image qualities used. The workaround for this is to edit your images in GIMP or Photoshop before using them in Scribus.
Although Scribus and Indesign are similar- Indesign’s file format (.indd) is proprietary and can NOT be read/opened/imported by Scribus. It’s currently unclear if Indesign has taken steps to be able to open Scribus files (.sla)
There are conversion processes that can be found by googling, but you may lose your layer functions and in some cases the whole of the file because it converts ‘every page’ of the file into a separate file*. As of today (10/30/13) Scribus is on version 1.4.3, with 1.5 in beta promising IDML files (the other export option Indesign offers besides pdf).