@winterschon For other favorites:
Calendar: I love remind(1), a CLI calendar that is more powerful than any other calendar I've ever used. It's a little rough sharing events externally or importing external events (I see you CalDAV note), but for our household, it's great, and I wrote up a detailed blog post² on how I use it (it's a little out of date now, but still works).
Finances: I track mine in ledger(1), largely compatible with hledger(1). There's also BeanCount with its web UI, Fava, but I'm less familiar with that. I'm wary of handing all our household financial data over to some 3rd party, but I do want insights into our spending, saving, etc, so #plaintextaccounting is handy for that
Todos: some folks prefer TaskWarrior³ which is the 900lb gorillia in the CLI todo-tracking game, but I prefer simple todo.txt-style⁴ todo lists, and I symlink my todo.txt file to my ~/.plan so I can use finger(1) to get my todo list remotely.
They all have the advantage of storing all their data in #plaintext, meaning I can track it in git and sync it around between machines.
That said, I know CLI apps aren't everybody's cup of tea, but they fit my brain and I like keeping everything local. And they're all light on resources, so even the wimpiest RPi runs them fine.
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¹ https://dianne.skoll.ca/projects/remind/
² https://blog.thechases.com/posts/remind/
³ https://taskwarrior.org/
⁴ https://github.com/todotxt/todo.txt-cli
Brings all the benefits of plain-text files (track them in git and sync them, use any $EDITOR you want to manipulate them, use standard Unix tools like grep/sed/awk and shell-functions to manipulate them, they compress well, etc)