[namibj]

GeoGebra is the closest I know, at least when limiting to copyleft [or theoretically the SQLite model would be fine, but it's pretty unique in dependability and selflessness for open source projects not subject to copyleft] "middle/high school (constructive?) geometry & function graphing teaching aid" classroom-grade robustness: bored & curious children are somewhat creative in their play/"(ab)use" of teaching/classroom software: buggy/anti-intuitive software can't survive the combination of:

- bored curious children playing around, bright and capable curious children exploring (way) beyond what the teacher explained, - normal students just getting by with the topic and relying on the software to aid their subject matter comprehension, - and teachers trying to plan lessons around it where they have to rely on it not needing a tutorial because there wouldn't really be time for such in the curriculum schedule.

[Xerox9213]

One of my favourite things about (desktop) Geogebra is its ability to export to tikz. Making complicated geometric shapes in a latex file can be done so easily with Geogebra. Perhaps not as elegant as Castel, but still quite nice.

https://castel.dev/post/lecture-notes-1/