LibreOffice - Writer - Open-source cross-platform word processor.
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.
Microsoft Word - Microsoft Word is a commercial word document processor for Windows.
PDFShift - Convert any HTML documents to high-fidelity PDF using a single POST request
Google Docs - Create a new document and edit with others at the same time -- from your computer, phone or tablet. Get stuff done with or without an internet connection. Use Docs to edit Word files. Free from Google.
Tcpdf - TCPDF: Open Source PHP Class for generating PDF documents