What are the opensource options available for creating professional looking e-books?
Are there a set of techniques/best-practices for this?
Please give inputs or direct me to precise sites that address this ...
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There are fantastic open source softwares for creating any kind of ebook. Depending up on the type of content you are working with, you could use a combination of them.
Scribus - DTP software, (used for creating Ubuntu's Full Circle magazine) Inkscape and Gimp can be used to create/design stuff. LaTeX produces stunning pdf files. The list is endless.
Now, one could write in a plain text file with some markdown, and convert it to any format (latex, latex->pdf, epub, html pages, slideshows..) using Pandoc or Calibre. This is probably the easiest way.
This site has some great info on doing that for ebook readers