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.
HTTrack - HTTrack is a free (GPL, libre/free software) and easy-to-use offline browser utility.
PDFShift - Convert any HTML documents to high-fidelity PDF using a single POST request
WebCopy - Cyotek WebCopy is a free tool for copying full or partial websites locally onto your harddisk for offline viewing.
Tcpdf - TCPDF: Open Source PHP Class for generating PDF documents
SiteSucker - SiteSucker is a Macintosh application that automatically downloads Web sites from the Internet.