PDFCrowd - Pdfcrowd is a Web/HTML to PDF online service. Convert HTML to PDF online in the browser or in your PHP, Python, Ruby, .NET, Java apps via the REST API.

Qt - Powerful, flexible and easy to use, Qt will help you not only meet your tight deadline, but also reduce the maintainable code by an astonishing percentage.

DocRaptor - As the only API powered by the Prince HTML-to-PDF engine, DocRaptor provides the best support for complex PDFs with powerful support for headers, page breaks, page numbers, flexbox, watermarks, accessible PDFs, and much more

JUCE - JUCE is a wide-ranging C++ class library for building rich cross-platform applications and plugins...

PDFShift - Convert any HTML documents to high-fidelity PDF using a single POST request

FLTK - Fast Light Toolkit - Fast Light Toolkit (FLTK)