Charles Proxy - HTTP proxy / HTTP monitor / Reverse Proxy
E2Guardian - Web filtering solution
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.
pfSense - pfSense is a free and open source firewall and router that also features unified threat management, load balancing, multi WAN, and more
Weer - A HTTP protocol debugger with Chrome DevTools frontend interface
CacheGuard-OS - CacheGuard is an enterprise grade Web Gateway solution offering Web Security & Optimization in the same box. Price starting at $99 per Year!