You are absolutely right, there are many options which we looked at before we began with the project. None of existing solutions provided the features we needed:

Authentication and authorization to meet our compliance needs, a satisfactory UI/UX, message streaming with JavaScript filters and a couple more features. We thought we can do better and just started hacking something. There's a lot more to come. I'll create a blog post describing in more detail why we've created Kowl.