Little Snitch - Little Snitch is a firewall application that monitors and controls outbound internet traffic.

Surge for Mac - Advanced Web Debugging Proxy for Mac & iOS

TripMode - Manage your Mac's broadband usage while on a hotspot

Charles Proxy - HTTP proxy / HTTP monitor / Reverse Proxy

Radio Silence - Radio Silence is a network monitor and firewall for the macOS. The software stops apps from making network connections. The firewall runs in the background and does not require an open window.

mitmproxy - mitmproxy is an SSL-capable man-in-the-middle proxy for HTTP.