Some random historical fun facts: Things Every Hacker Once Knew
Shorthand is a random hobby of mine that seems a bit unrelated to my other interests. I write daily (by hand) using Gregg Shorthand, and I occasionally practice machine shorthand too. I think it's cool to learn about how court-reporters (and office secretaries back in the day), record text in a more efficient way.
For written shorthand, I would recommend learning Gregg Simplified out of the Gregg series, since Simplified does not have too high of a memory burden, yet still allows for pretty fast speeds. You can find manuals online at places like the shorthand subreddit (also includes discussions about non-Gregg shorthands) or this Gregg Shorthand Site. Richard Liu made a cool online dictionary for Gregg Shorthand, although you can also find dictionaries in pdf form online.
For machine shorthand, Plover is definitely the best steno software (commercial software is expensive!), and I would recommend the tinymod as a machine (open source hardware!). Learn Plover is a good site to learn about machine shorthand theory.