I use a pencil, ruler, and piece of paper. No symbols to download, no learning curve beyond basic electronics, and no manufacturer influences. It's nice to have a handy book of all the symbols for those I can't remember because they are not used as often.
It would be nice to have a stencil that has these symbols on them. Perhaps someone can make a fortune with one of these.
If I want to upload my work I can scan it or take a picture.
I once heard a story, maybe true or fiction I don't know, about the US and Russian space program. The US spent billions developing a pen that would work in zero gravity and at any angle on almost any paper. The Russians used a pencil.
Why re-invent the wheel? If you do a heck of a lot of drawings I can see the need for a cad program to simplify things and keep uniformity. Otherwise your wasting valuable time you could spend making your drawing a working piece. A good engineer doesn't care if it is drawn on a napkin so long as it works as intended.
Could we with ink the ocean fill and were the skies of parchment made, Were every stalk on earth a quill and every man a scribe by trade. To write the love of God above would drain the oceans dry, nor could the scroll contain the whole though stretched from sky to sky.