Paros and Zed Attack Proxy (ZAP)
Paros is a Java based HTTP/HTTPS proxy for assessing web application vulnerability. It supports editing/viewing HTTP messages on-the-fly. The application has not been updated for several years.
Zed Attack Proxy (ZAP) is another web proxy that has more recent releases.
https://www.owasp.org/index.php/OWASP_Zed_Attack_Proxy_Project