NetTool is a developer tool for monitoring and manipulating
application-level network messages, particularly useful for debugging
web applications and web services. There are two components to
NetTool: the HTTP Client, and the TCP Tunnel.¹

Paros is for web application security assessment. It is free of
charge and completely written in Java. Through Paros's proxy nature,
all HTTP and HTTPS data between server and client, including cookies
and form fields, can be intercepted and modified.²

^{1Source:Sourceforge}

^{1Source:Paroproxy}