- Legacy DITA to PDF editing solution. It is no longer distribute with DITA OT 2.x and is probably not compatible anymore with it.
- Default DITA to PDF solution embedded in the DITA Open Toolkit distribution. Besides Apache FOP you can also use RenderX XEP or Antenna House for publishing. It's customization can be done either via a plugin or via a PDF customization folder: https://www.oxygenxml.com/doc/versions/17.1/ug-editor/index.html#topics/dita_pdf_output_customization.html.
- DITA to PDF using CSS. This open source DITA OT plugin was developed by Oxygen as an alternative to the default PDF publishing. It allows styling the DITA content using CSS and publishing to PDF using either Prince XML or Antenna House.
- Antenna House DITA OT plugin for producing PDF from DITA using Antenna House. There is also a DITA specialization plugin which allows you to set specific formatting attributes directly to DITA elements.
- DITA to HTML 5 to PDF using CSS. This open source DITA OT Plugin publishes DITA to HTML5 and then passes the output to node-html-pdf. This plugins takes a HTML file as a parameter and returns a PDF document.
- The TopLeaf XML Publisher commercial product allows you to produce various outputs like PDF and EPUB from XML content. The application also has a visual PDF layout formatter, it comes also with a DITA OT plugin and has installation instructions for Oxygen:http://www.turnkey.com.au/tksweb/xmtp/webhelp_out/oxygen/install.html.
- Miramo, again a commercial solution which recently started developing support for DITA using a DITA OT plugin. Possibly user based DITA to PDF publishing will be free and server based production will require buying a license. Like TopLeaf, it also has a visual PDF layout designer.
- Adobe FrameMaker can also publish to PDF using its own solution.
Now the question would be, why there are so many solutions available? In my opinion all these solutions are available because the default DITA to PDF output still requires quite a lot of XSLT skills in order to customize. Jarno Elovirta's PDF plugin generator covers some of the mainstream possible customizations but not all.
What do you think?