Surge for Mac!

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.

mitmproxy is an SSL-capable man-in-the-middle proxy for HTTP. It provides a console interface that allows traffic flows to be inspected and edited on the fly. It also features mitmdump, a commandline tool that provides a tcpdump-like interface for saving, viewing and manipulating HTTP traffic.

Charles is an HTTP proxy / HTTP monitor / Reverse Proxy that enables a developer to view all of the HTTP and SSL / HTTPS traffic between their machine and the Internet. This includes requests, responses and the HTTP headers (which contain the cookies and caching information).

The Zed Attack Proxy (ZAP) is an easy to use integrated penetration testing tool for finding vulnerabilities in web applications.It is designed to be used by people with a wide range of security experience and as such is ideal for developers and functional testers who are new to penetration testing.ZAP provides automated scanners as well as a set of tools that allow you to find security vulnerabilities manually.

NetworkMiner is a Network Forensic Analysis Tool (NFAT) for Windows. NetworkMiner can be used as a passive network sniffer/packet capturing tool in order to detect operating systems, sessions, hostnames, open ports etc. without putting any traffic on the network. NetworkMiner can also parse PCAP files for off-line analysis and to regenerate/reassemble transmitted files and certificates from PCAP files.

The always-on web debugging proxy

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.

Andiparos is a fork of the famous Paros Proxy. It is an open source web application security assessment tool that gives penetration testers the ability to spider websites, analyze content, intercept and modify HTTP requests on-the-fly, etc.

Proxy.app is the perfect tool for debugging and analysing both HTTP requests and responses and modify data in transit. It can be used to debug hard problems while doing web development or as a penetration testing tool during security assessments.

Slowy is an OSX app which simulates custom connection's conditions and limits the network traffic. It is created for web developers that work on a local server, to test a website with a real-world connection.

AppScope is a tool for networked mobile applications to instantly capture comprehensive bug reports containing screen video, network data and system logs.