Wireshark - Wireshark is a network protocol analyzer for Unix and Windows. It lets you capture and interactively browse the traffic running on a computer network.
Web ScrapBook - A browser extension that captures the web page faithfully with highly customizable configurations.
tcpdump - tcpdump is a common packet analyzer that runs under the command line.
HTTrack - HTTrack is a free (GPL, libre/free software) and easy-to-use offline browser utility.
SmartSniff - SmartSniff is a packet sniffer that capture TCP/IP packets and display them as sequence of conversations between clients and servers.
Archivarix Website Downloader - Website online downloader and Content Management System (CMS) existing site converter.