https://wiki.contextgarden.net/
It's a monolithic kernel with a relatively sane collection of "setup" macros that, by and large, can accomplish much of what LaTeX and its packages can do.
If you're curious about how to build TeX from scratch, have a look at my TeX.SE answer:
https://tex.stackexchange.com/a/576314/2148
I'd imagine making a FOSS port in Rust that has non-cryptic error messages wouldn't be a multi-year project using modern GPTs.
[1] https://www.latex-project.org/latex3/
[2] https://github.com/latex3/latex3
If you're stuck on something LaTeX related, remember there's the latest edition to The LaTex Companion. It even has an appendix explaining the (in)famously cryptic LaTeX/TeX error messages:
https://latex-project.org/help/books/
There's also, among other resources, the great LaTeX Font Catalogue: https://tug.org/FontCatalogue/
Enjoy the new release!
[0]: https://tug.org/texlive/doc/texlive-en/texlive-en.html#x1-94...
[1]: https://www.latex-project.org/news/latex2e-news/ltnews.pdf#i...
https://www.tug.org/levels.html seems like a good start
Look for /texmf-dist/doc/fonts/memdesign/memdesign.pdf if you want a fun non-technical one.
The problem is that today we have a massive gap in development: there was a time when high-quality FLOSS development existed, followed by an era of resting on one's laurels while creating very little, mostly just stuff built on top of existing systems in an attempt to simplify things, which only resulted in making them more complex and fragile, with zero innovation.
Today, we have generations of developers who simply don't know classic FLOSS tools beyond the surface level and lack the technical background to create new ones that aren't dependent on the tech giants. This is because obsolete universities have de facto trained legions of big tech labourers rather than autonomous technicians capable of standing on their own two feet.
The issue is that there was never a real desire to give "the power of computing" to end users. Consequently, at the first opportunity, the desktop was undermined and rejected to keep everyone dependent on someone else's services. Now, young developers don't know how to evolve back towards the desktop, even though they sense, without fully understanding, that this is the right way forward.
We are losing decades of potential evolution with repercussions for centuries to come, just to feed a handful of people who profit from others' ignorance.
So, while it's true that on one hand we have excellent tools that are obsolete, clunky, and difficult to integrate today, it's also true that on the other hand we have a void. This is because the foundations of modern software are flawed and unsustainable, created solely for the interests of Big Tech. Either we move past this or we head for ruin, as has been happening for some time now; eventually, it will be impossible to carry on and we'll have to start again from scratch, with enormous costs, delays, and damage.
The system is flexible and simple.
Used TeX for the same and had to lose sanity for it to even work semi well.