WebSiteSniffer!

Wireshark is the world's foremost network protocol analyzer. It lets you capture and interactively browse the traffic running on a computer network. It is the de facto (and often de jure) standard across many industries and educational institutions.

Fiddler is a Web Debugging Proxy which logs all HTTP(S) traffic between your computer and the Internet. Fiddler allows you to inspect all HTTP(S) traffic, set breakpoints, and "fiddle" with incoming or outgoing data. Fiddler includes a powerful event-based scripting subsystem, and can be extended using any .NET language.

Cyotek WebCopy is a free tool for copying full or partial websites locally onto your harddisk for offline viewing.

tcpdump is a common packet analyzer that runs under the command line. It allows the user to intercept and display TCP/IP and other packets being transmitted or received over a network to which the computer is attached.

MetaProducts Offline Explorer is a Windows NT/2000/XP/2003/Vista program that allows you to download an unlimited number of your favorite Web and FTP sites for later offline viewing, editing or browsing.

grab-site is a crawler for archiving websites to WARC files. It includes a dashboard for monitoring multiple crawls, and supports changing URL ignore patterns during the crawl.

SiteSucker is a Macintosh application that automatically downloads Web sites from the Internet. It does this by asynchronously copying the sites Web pages, images, backgrounds, movies, and other files to your local hard drive.

WebZIP Offline Browser - a fast and easy way to download, store and browse Web sites offline.

Wysigot is far more than just a simple off-line browser!

Website Downloader lets you download an entire website, assets and all.

apptalk.ninja is a great, easy-to-use tool for app developers tackle that monitors and debugs issues with their apps’ communication over-the-air.

WebCopier is an easy-to-use website mirror utility. It allows to download entire Web sites, store them locally and view them later, at users' convenience. WebCopier provides access to the downloaded information at any time, no matter where its users are, no Internet connection is required. WebCopier can copy or print whole sites or sections. Your saved pages can be copied onto disks and CDs, so you can take your Web-snapshot with you. Companies can use WebCopier to transfer company's intranet contents to staff desktops and notebooks, create a copy of companies' online catalogs and brochures for sales personal, backup corporate web sites, print downloaded files. Individuals can use WebCopier to save complete copies of their favorite sites, magazines, or stock quotes. NewsCopier - RSS newsreader puts the latest headlines, weather, sports, business, and entertainment news right in your hands. »

Wpull is a wget-compatible web downloader and crawler with WARC and Python/Lua scripting support