This is just just excellent. I do a lot of ETL work and need to build custom workflows for it, this is exactly what I have been looking for. Good job, team!
Since you brought up ETL, you may also be interested in Meltano (https://meltano.com), an open source ETL tool we've been working on at GitLab for a few years now!
Thanks! Give it a go and let us know if there's anything we can do to make this better. We let you export Python code that maps 1-to-1 to any processing step you take on the UI.
I shared some thoughts on how it compares to DropBase in another comment: https://news.ycombinator.com/edit?id=24194916
If you end up giving it a try, I'd love to hear what you think :)