Apart from technology (Go instead of JavaScript) the main difference is that Slang aims to be completely visual. Many tools that exist call themselves flow-based but require coding in the end, at least for individual components. I wrote an article comparing Node-RED and Slang. You can find it here: Slang and Node-RED, a Comparison

Right now, there is not much documentation or a feature overview, so you understandably opened this issue. Currently, we are working on a new user interface which consumes most of our time. But of course we know this is crucial and will definitely provide detailed information in the future.

@dumblob In the mean time we released documentation at https://bitspark.de/slang/docs/
Are you currently using any of those alternatives in production?

I've looked at the documentation and it looks quite complex - do you have any practical (not just functional) examples? Feel free to get inspiration from examples for NoFlo (Node-RED has also some good examples even though Node-RED itself is quite limited compared to other flow programming environments/languages).