Surge for Mac - Advanced Web Debugging Proxy for Mac & iOS
ModSecurity - ModSecurity is an Open Source web application firewall developed by Trustwave's SpiderLabs.
Charles Proxy - HTTP proxy / HTTP monitor / Reverse Proxy
Shadow Daemon - Shadow Daemon is a collection of tools to detect, record and prevent attacks on web applications.
HTTP Toolkit - Beautiful, cross-platform & open-source tools to debug, test & build with HTTP(S). One-click setup for browsers, servers, Android, CLI tools, scripts and more.
ironbee - Universal web application firewall engine