This is similar to an idea I once had about spreadsheets. In my mind it was more focused on being able to handle bigger amounts of data in a more efficient way: a "block" would be a data source and could for example be linked to a database or something else instead of data in spreadsheet cells.

In any case, I think this looks really good.

What I personally would find handy, is if there would be a way to show that one block depends on data from another block. I think it will be common that several blocks will be pure input and other blocks will be pure output. It should be doable to show direct dependencies for a block and the transitive dependencies for a block.

A separate input box for editing cells might also be useful.

I like that it runs in a browser, but I would appreciate if there is a way to run the software locally and store the data locally. And like I said, I would like to see a way to define blocks that connect to a data source, such as a database running locally on my machine.