Node-RED is an awesome open-source tool for stream processing.
You can drag and drop "nodes" into your workflow, that can do things from processing a twitter stream to calling functions to sentiment analysis and automation.
All this is done with a visual drag and drop tool. No code to write (unless you want to)! Very powerful for simple to very advanced use cases.
Here's the command to run to launch Node-RED. Just make sure you have Docker installed.
docker run -it -p 1880:1880 -v $(pwd)/.node-red:/data --name mynodered nodered/node-red
After running the command above, just point your browser to http://localhost:1880
to see the dashboard.
Here are some links for more information.