Proxie is described as 'A HTTP Debugging Proxy for MacOS' and is a HTTP(S) Debugger in the Development category. There are seven alternatives to Proxie for a variety of platforms, including Mac, Windows, Linux, Online / Web-based and iPhone. The best alternative is Fiddler, which is free. Other great apps like Proxie are mitmproxy (Free, Open Source), Charles (Paid), HTTP Toolkit (Freemium, Open Source) and Proxyman (Paid).
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.
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).
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.