Charles Proxy - HTTP proxy / HTTP monitor / Reverse Proxy
Web ScrapBook - A browser extension that captures the web page faithfully with highly customizable configurations.
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.
HTTrack - HTTrack is a free (GPL, libre/free software) and easy-to-use offline browser utility.
Postman - The Collaboration Platform for API Development
Archivarix Website Downloader - Website online downloader and Content Management System (CMS) existing site converter.