What it is
Intercept (“man-in-the-middle”) proxy.
Where to find it
Source: https://github.com/mitmproxy/mitmproxy
Site: https://mitmproxy.org
My thoughts
It seems really cool, but using it to intercept and modify server responses (my main use for it) has proven quite cumbersome. Still, the TUI is actually really good as far as TUIs go.