Colasoft Capsa is not available for Mac but there are a few alternatives that runs on macOS with similar functionality. The best Mac alternative is Wireshark, which is both free and Open Source. If that doesn't suit you, our users have ranked more than 10 alternatives to Colasoft Capsa and four of them are available for Mac so hopefully you can find a suitable replacement. Other interesting Mac alternatives to Colasoft Capsa are tcpdump (Free, Open Source), Ettercap (Free, Open Source) and packeth (Free, Open Source).
Wireshark is the world's foremost network protocol analyzer. It lets you capture and interactively browse the traffic running on a computer network. It is the de facto (and often de jure) standard across many industries and educational institutions.
tcpdump is a common packet analyzer that runs under the command line. It allows the user to intercept and display TCP/IP and other packets being transmitted or received over a network to which the computer is attached.
packeth is GUI and CLI packet generator tool for ethernet. Primary it is developed and maintained for Linux, but some ports for Windows and MAC have also be done. It allows you to create and send any possible packet or sequence of packets on the ethernet link.