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.
PDFreactor - PDFreactor is a cross-platform enterprise-grade HTML to PDF conversion engine.
PDFShift - Convert any HTML documents to high-fidelity PDF using a single POST request
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
pdflayer - Free, powerful HTML to PDF API supporting both URL and raw HTML conversion. Unlimited document size, lightning-fast and compatible PHP, Python, Ruby, etc.
Tcpdf - TCPDF: Open Source PHP Class for generating PDF documents