Polipo - A small and fast caching web proxy (a web cache, an HTTP proxy, a proxy server).
Charles Proxy - HTTP proxy / HTTP monitor / Reverse Proxy
Artica Proxy - Artica Proxy is an appliance that claim to manage Squid-cache proxy with all features that Squid...
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.
Privoxy - Privoxy helps users to protect their privacy.
Weer - A HTTP protocol debugger with Chrome DevTools frontend interface