If not a "large number", then more like a "huge number".

Even the single application Blender itself has several different visual node based programming systems (most but not all built on top of the same framework, and applied to different kinds of programming), for shader programming, CPU image processing, video compositing, lighting, animation and constraints, particle systems, physics simulations, procedural mesh generation, and the Blender Foundation and third parties are developing even more, like procedural city generation:

Procedural city generation:

https://www.youtube.com/watch?v=jb_jwsyfQc4&ab_channel=derbe...

Everything nodes:

https://code.blender.org/2020/12/everything-nodes-and-the-sc...

Nodes Workshop - 22 - 25 June 2021

https://devtalk.blender.org/t/nodes-workshop-22-25-june-2021...

>“It is like compositor but for physics”.

The complete beginners guide to Blender nodes, Eevee, Cycles and PBR:

https://artisticrender.com/the-complete-beginners-guide-to-b...

>Blender has a few nodes systems. The first and obvious one is Blenders shading system for Cycles and Eevee. This is the node system that we will focus on in this article.

>But we also have nodes for compositing, lighting and textures, even if the use case and future for texture nodes are uncertain at this point.

>We can also extend Blender with other node systems through add-ons. The most well-known is probably animation nodes that come bundled with Blender.

>There are also other node systems available for Blender. AMD ProRender for example, a third-party render engine that has its own shader node system. Another example is Luxrender. There is also mTree for generating trees with nodes and Sverchok that can manipulate all kinds of data with nodes.

Reposting this from a few years ago:

https://news.ycombinator.com/item?id=18496880

There's so much interesting prior work!
I really enjoyed this paper “A Taxonomy of Simulation Software: A work in progress” from Learning Technology Review by Kurt Schmucker at Apple. It covered many of my favorite systems.

http://donhopkins.com/home/documents/taxonomy.pdf

It reminds me of the much more modern an comprehensive "Gadget Background Survey" that Chaim Gingold did at HARC, which includes Alan Kay's favorites, Rockey’s Boots and Robot Odyssey, and Chaim's amazing SimCity Reverse Diagrams and lots of great stuff I’d never seen before:

http://chaim.io/download/Gingold%20(2017)%20Gadget%20(1)%20S...

I've also been greatly inspired by the systems described in the classic books “Visual Programming” by Nan C Shu, and “Watch What I Do: Programming by Demonstration” edited by Alan Cypher.

https://archive.org/details/visualprogrammin00shu_2pf

https://archive.org/details/watchwhatido00alle

Brad Myers wrote several articles in that book about his work on PERIDOT and GARNET, and he also developed C32:

C32: CMU's Clever and Compelling Contribution to Computer Science in CommonLisp which is Customizable and Characterized by a Complete Coverage of Code and Contains a Cornucopia of Creative Constructs, because it Can Create Complex, Correct Constraints that are Constructed Clearly and Concretely, and Communicated using Columns of Cells, that are Constantly Calculated so they Change Continuously, and Cancel Confusion

http://www.cs.cmu.edu/~bam/acronyms.html

Also, here's an interesting paper about Fabrik:

https://donhopkins.com/home/Fabrik%20PE%20paper.pdf

Danny Ingalls, one of the developers of Fabrik at Apple, explains:

"Probably the biggest difference between Fabrik and other wiring languages was that it obeyed modular time. There were no loops, only blocks in which time was instant, although a block might ’tick’ many times in its enclosing context. This meant that it was real data flow and could be compiled to normal languages like Smalltalk (and Pascal for Apple at the time). Although it also behaved bidirectionally (e.g. temp converter), a bidirectional diagram was really only a shorthand for two diagrams with different sources (this extended to multidirectionality as well)"