I use GnuCash for two companies and personal accounting. Love it.
jbd
I use fish shell only now. Used to only write bash, but I've started writing some fish scripts. I wouldn't try to plan too much WRT shell scripting up front. Just fix your pain points as you go.
I use Calibre and its web server locally. Works great.
I use emacs, Denote, and markdown-mode to keep a loose Zettlekasten archive of notes.
I use and recommend Free File Fillable Forms. https://www.freefilefillableforms.com It's basically filling out an electronic version of the paper forms, but some fields are auto-calculated.
I noticed that some of these are apps and some are protocols. It makes sense to list the app if the protocol is proprietary, but it's confusing that there can be multiple apps for an open protocol and not all of those apps could feature the same level of privacy.
I'm just learning about all this. Looks like P2P is what I want. Thanks