Surge for Mac - Advanced Web Debugging Proxy for Mac & iOS
Polipo - A small and fast caching web proxy (a web cache, an HTTP proxy, a proxy server).
Weer - A HTTP protocol debugger with Chrome DevTools frontend interface
Squid Proxy - Website Content Acceleration and Distribution. Thousands of web-sites around the Internet use Squid to drastically increase their content delivery. Squid can reduce your server load and improve delivery speeds to clients.
Cellist - Cellist is an all-in-one HTTP debugging proxy software designed for OS that provides a straightforward approach to put a proxy between the HTTP client and the internet.
ExaProxy - ExaProxy is a a high-performance non-caching proxy.