NetTool was one of my early open-source projects. I first created it (in Java & Swing) in the late nineties (98/99) to debug HTTP and TCP traffic. It has since been long neglected, but in some ways it’s a spiritual ancestor of later projects like Postman. I’ve no qualms about saying it: at the time, NetTool was pushing the boundaries of great Swing design.

NetTool HTTP Client

NetTool TCP Tunnel

• NetTool page on SourceForge
• SourceForge project page

At last count, it had over 100K downloads from SourceForge.