The package sisu contains a few documents published under the GPL or that are
Debian Free Software Guideline license compatible, noteably:

  Text: Free as in Freedom - Richard Stallman's Crusade for Free Software
    URL: <http://faifzilla.org/>
  Author: Sam Williams
  Copyright: Sam Williams 2002
  License: Permission is granted to copy, distribute and/or modify this
    document under the terms of the GNU Free Document License, Version 1.1 or
    any later version published by the Free Software Foundation; with the
    Invariant Sections being no invariant sections, with the Front-Cover Texts
    being no invariant sections, and with the Back-Cover Texts being no
    invariant sections URL: <http://www.gnu.org/copyleft/fdl.html>
  Markup: free_as_in_freedom.richard_stallman_crusade_for_free_software.sam_williams.sst

  Text: Free as in Freedom 2.0 - Richard Stallman and the Free Software Revolution
    URL: <http://faifzilla.org/>
  Author: Sam Williams, Richard M. Stallman
  Copyright: Sam Williams, Richard Stallman 2010
  License: Permission is granted to copy, distribute and/or modify this
    document under the terms of the GNU Free Document License, Version 1.1 or
    any later version published by the Free Software Foundation; with the
    Invariant Sections being no invariant sections, with the Front-Cover Texts
    being no invariant sections, and with the Back-Cover Texts being no
    invariant sections URL: <http://www.gnu.org/copyleft/fdl.html>
  Markup: free_as_in_freedom_2.richard_stallman_and_the_free_software_revolution.sam_williams.richard_stallman.sst

Output in multiple formats can be generated running SiSU against the markup
samples, e.g.:

sisu --html filename.sst
sisu --html --epub --pdf filename.sst

Online a few sample marked up documents, and their resulting outputs, can be
found at:
 <http://www.jus.uio.no/sisu>
 <http://www.jus.uio.no/sisu/SiSU/examples.html>

A few additional sample books prepared as sisu markup samples, output formats
to be generated using SiSU are contained in a separate package
sisu-markup-samples

sisu-markup-samples contains books (prepared using sisu markup), that were
released by their authors various licenses mostly different Creative Commons
licences that do not permit inclusion in the Debian Project as they have
requirements that do not meet the Debian Free Software Guidelines for various
reasons, most commonly that they require that the original substantive text
remain unchanged, and sometimes that the works be used only non-commercially.

  Free as in Freedom - Richard Stallman's Crusade for Free Software, Sam
  Williams, [as above]

  Free as in Freedom  2.0 - Richard Stallman and the Free Software Revolution,
  Sam Williams, Richard M. Stallman [as above]

  Text: Free Culture - How Big Media Uses Technology and the Law to Lock Down Culture and Control Creativity
    URL: <http://www.free-culture.cc>
  Author: Lawrence Lessig
    URL: <http://www.lessig.org/>
  Copyright: Lawrence Lessig, 2004
  License: Attribution-Noncommercial (CC-BY-NC) 1.0
    URL: <http://creativecommons.org/licenses/by-nc/1.0/>
  Markup: free_culture.lawrence_lessig.sst

  Text: The Wealth of Networks - How Social Production Transforms Markets and Freedom
    URL: <http://cyber.law.harvard.edu/wealth_of_networks/Main_Page>
  Author: Yochai Benkler
    URL: <http://www.benkler.org/>
  Copyright: 2006 Yochai Benkler
  License: Attribution-Noncommercial-Share Alike (CC-BY-NC-SA) 2.5
    URL: <http://creativecommons.org/licenses/by-nc-sa/2.5/>
  Markup: the_wealth_of_networks.yochai_benkler.sst

  Text: Democratizing Innovation
    URL: <http://web.mit.edu/evhippel/www/democ1.htm>
  Author: Eric von Hippel
    URL: <http://web.mit.edu/evhippel/www/>
  Copyright: 2005 Eric von Hippel
  License: Attribution-Noncommercial-No Derivative Works (CC-BY-NC-ND) 2.0
    URL: <http://creativecommons.org/licenses/by-nc-nd/2.0/>
  Markup: democratizing_innovation.eric_von_hippel.sst

  Text: Viral Spiral
    URL: <http://viralspiral.cc/>
  Author: David Bollier
    URL: <http://www.bollier.org/>
  Copyright: 2008 David Bollier
  License: Attribution-Noncommercial (CC-BY-NC) 3.0
    URL: <http://creativecommons.org/licenses/by-nc/3.0/>
  Markup: viral_spiral.david_bollier.sst

  Text: Two Bits - The Cultural Significance of Free Software
    URL: <http://twobits.net/>
  Author: Christopher Kelty
    URL: <http://kelty.org/>
  Copyright: Duke University Press, 2008
  License: Attribution-Noncommercial-Share Alike (CC-BY-NC-SA) 3.0
    URL: <http://creativecommons.org/licenses/by-nc-sa/3.0/>
  Markup: two_bits.christopher_kelty.sst

  Text: The Public Domain - Enclosing the Commons of the Mind
    URL: <http://www.thepublicdomain.org/>
  Author: James Boyle
    URL: <http://james-boyle.com/>
  Copyright: James Boyle, 2008
  License: Attribution-Noncommercial-Share Alike (CC-BY-NC-SA) 3.0
    URL: <http://creativecommons.org/licenses/by-nc-sa/3.0/>
  Markup: the_public_domain.james_boyle.sst
    Note: the book index has not yet been included

  Text: Free For All - How Linux and the Free Software Movement Undercut the High Tech Titans
    URL: <http://www.wayner.org/books/ffa>
  Author: Peter Wayner
    URL: <http://www.wayner.org>
  Copyright: Peter Wayner, 2000
  License: Attribution-Noncommercial (CC-BY-NC) 1.0
    URL: <http://creativecommons.org/licenses/by-nc/1.0/>
  Markup: free_for_all.peter_wayner.sst

  Text: The Cathederal and the Bazaar
    URL: <http://www.catb.org/~esr/writings/cathedral-bazaar/cathedral-bazaar/>
  Author: Eric Raymond
    URL: <http://www.catb.org/~esr>
  Copyright: Eric S Raymond, 2000
  License:  Open Publication License, v 2.0
    URL:
  Markup: the_cathedral_and_the_bazaar.eric_s_raymond.sst

  Text: CONTENT - Selected Essays on Technology, Creativity, Copyright and the Future of the Future
    URL: <http://craphound.com/content>
  Author: Cory Doctorow
    URL: <http://craphound.com>
  Copyright: Cory Doctorow, 2008
  License: Attribution-Noncommercial-Share Alike (CC-BY-NC-SA) 3.0
    URL: <http://creativecommons.org/licenses/by-nc-sa/3.0/>
  Markup: content.cory_doctorow.sst

  Text:  Down and Out in the Magic Kingdom
    URL: <http://craphound.com/down>
  Author: Cory Doctorow
    URL: <http://craphound.com>
  Copyright: Cory Doctorow, 2003
  License: Attribution-NonCommercial-ShareAlike (CC-BY-NC-SA) 1.0
    URL: <http://creativecommons.org/licenses/by-nc-sa/1.0/>
  Markup: down_and_out_in_the_magic_kingdom.cory_doctorow.sst

  Text: Little Brother
    URL: <http://craphound.com/littlebrother>
  Author: Cory Doctorow
    URL: <http://craphound.com>
  Copyright: Cory Doctorow, 2008
  License: Attribution-Noncommercial-Share Alike (CC-BY-NC-SA) 3.0
    URL: <http://creativecommons.org/licenses/by-nc-sa/3.0/>
  Markup: little_brother.cory_doctorow.sst
  Illustration: little_brother_doctorow.png
    URL: <http://commons.wikimedia.org/wiki/File:Little_Brother_illustration_by_Richard_Wilkinson_04.jpg>
  Copyright: Richard Wilkinson
  License: Attribution United States (CC BY) 3.0
    URL: <http://creativecommons.org/licenses/by/3.0/us/>

  Text: For the Win
    URL: <http://craphound.com/ftw>
  Author: Cory Doctorow
    URL: <http://craphound.com>
  Copyright: Cory Doctorow, 2010
  License: Attribution-Noncommercial-Share Alike (CC-BY-NC-SA) 3.0
    URL: <http://creativecommons.org/licenses/by-nc-sa/3.0/>
  Markup: for_the_win.cory_doctorow.sst

  Text: Accelerando
    URL: <http://www.accelerando.org/>
  Author: Charles Stross
    URL: <http://www.antipope.org/charlie/>
  Copyright: Charles Stross, 2005
  License: Attribution-Noncommercial-No Derivative Works (CC-BY-NC-ND) 2.0
    URL: <http://creativecommons.org/licenses/by-nc-nd/2.0/>
  Markup: accelerando.charles_stross.sst
    Note: The SiSU preparation (presentations) of Accelerando are done with the kind permission of the author Charles Stross

  Text: UN Contracts for International Sale of Goods
  Author: UN, UNCITRAL
    URL: <http://www.un.org/>
  Copyright:
  License:
  Markup: un_contracts_international_sale_of_goods_convention_1980.sst

Most additional material contained in sisu-markup-samples were published under
various Creative Commons licenses, check the rights section of each document
for the copyright and license, or the COPYRIGHT file associated with the
package for a listing of material and their associated licenses.

A few document more markup samples can be found at
  <http://www.sisudoc.org>
  <http://www.jus.uio.no/sisu>
  <http://www.jus.uio.no/sisu/SiSU/examples.html>