Unfunded is kind of a stretch, but at least libxml2.
Essentially "povertyware" as you call it when you consider the trillion dollar companies built on top of them? Now that's way easier: SQLite, PostgreSQL, ffmpeg, imagemagick, numpy, pandas, GTK, curl, zlib, libpng, zxing or any other popular qr/barcode library, etc...
I'd say the Gentoo handbook comes pretty close. You set up everything in the system and all is well explained. Not quite as extreme as LFS but enough to learn and not punish yourself.
My mileage was quite different: last time I tried, scrolling too fast with the mouse wheel consistently caused a segfault.