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Interesting, and clearly a lot of work's gone into this (60,000 lines of Typescript), particularly the UI, which is impressive (if, sometimes, over the top). I've been developing a similar system (http://www.fmjlang.co.uk/fmj/tutorials/TOC.html) and it's interesting to note the similarities and differences.
Similarities: code as directed graphs (less obvious in FMJ); can only connect outputs to units of compatible type; if and wait (looping is handled differently); sticky values; sliders. These design decisions are practically forced on you, but are often absent in earlier visual dataflow languages (e.g. Prograph, LabVIEW).
Differences: (1) inputs are named in Unit, ordered in FMJ (though they're named in formulas and edges can be labelled). (2) I experimented with automatic code layout but found this was too slow and not always what I wanted. Well done for getting this to work. (3) FMJ is now fully homoiconic - this maybe isn't a priority for Unit.
The Unit design philosophy is explained in https://github.com/samuelmtimbo/unit/blob/main/src/docs/conc... . This doesn't mention earlier approaches (e.g. the Manchester Dataflow Computer, Prograph) and it seems to be based on vaguely similar ideas developed more recently (Morrison's Flow Based programming; possibly React and similar systems for web development - I'm unfamiliar with these).
I have a number of questions:
(1) How does the type system work? Is it Dependently typed, Hindley-Milner, or something more basic? (FMJ is Hindley-Milner, with dependent typing partially implemented). How are new types be defined?
(2) How is the visual representation stored? One criticism I faced was that people wanted a readable textual representation which would work well with existing version control systems, a problem I have now largely solved.
(3) How are runtime errors handled?
(4) Is recursion supported? (I assume yes, but I didn't see any examples.) What about macros?
(5) What does Unit compile to? (FMJ has an experimental compiler where programs are compiled by running their source without evaluating their inputs, output is Lisp.)