Looks very good. I have been using some CLI like https://github.com/esphen/wsta/ but definetely a GUI like this is better.

This is why I also hate socket.io, it's not a raw socket to just simply connect and start sending raw payload.

One of the suggestions that came up more often from people who tried out Socket Wrench was the ability to connect to Socketio servers. However supporting socketio namespaces complicated the UX, so I decided to wait till I got a lot more people asking for SocketIO support to implement it.

Would love to be able to use this with socket.io

I've created a new issue (https://github.com/asleepysamurai/socketwrench/issues/2) to track this. If it get's enough votes from other users, I'll add it.

Now need one for kafka!

Does kafka not have something similar to RabbitMQ's management plugin?

Where's the source?

It's not open source. I want to keep any possibility of future monetization open for now.