I'd love if Inkscape implemented Xfig technical drawing features.
I appreciate the exhausting amount of work that goes into something like Inkscape, but holy crap. Segfaulting on me. Or leaving a foregrounded window open with no content in it that I can't close and that blocks the rest of the program until I kill -9 it. Very frustrating when I was trying to get real work done.
The 1.2 release is expected in a few days (and it has many features with a ton of bug fixes).
* tangent/normal to a curve: there is an experimental Live Path Effect for tangent (You can get the normal by just rotating the tangent 90 degrees)
* Measure length: Many ways to get that: e.g. the measure tool. or you can use the Measure segments Live Path Effect.
* Measuring the area: There is an extension: Extensions > Visualize Path > Measure Path.
* Measuring angles: again, you can use the measure tool.
* Library of elements: Inkscape has symbols Objects > Symbols. You can also add you own symbols. See also https://github.com/PanderMusubi/inkscape-open-symbols
* Inkscape snapping is way better (See the new smart alignement snapping in version 1.2).
* Inkscape also prints instructions on how to use tools on the status bar
Another thing I miss in inkscape (in case you know): I sometimes did some very interesting interactive live geometric demonstrations with Kig. Had inkscape had the same features, I'd use it.
Anyway. You may find this post interesting: https://castel.dev/post/lecture-notes-2/
Also, I wrote a small library that lets me programmatically generate SVGs with Python. This lets me create very precise vector images. This fills some of the same needs.