As in title, preferably open-source, but doesn’t have to, I will start:
KOReader - Amazing reader app, and being able to use the same app across various devices, even non-android ones, is pure bliss. Japanese support is pretty good too, which makes me happy. Though… Sadly no vertical text support :c
Syncthing-fork - Being able to keep a library of books, and some files, and easily keep the shared folder across various devices, is mega comfy. Tachiyomi - Cute manga reader.
NewPipe - Really pleasant youtube client, that i sometimes use to listen to things in the background.
Kaku - An useful Japanese OCR app, that works… quite decently for when I encounter kanji that I do not recognize, and is not text.
EinkBro - A web browser, that on e-ink devices, is quite comfy. Has few… quirks, but works well on e-ink
Torque. It allows you to connect to your car’s OBD2 port via a cheap Bluetooth adapter. From the app, you can read and clear diagnostic codes, setup custom gauges, and log data. It was very helpful when my alternator was dying and when my car was overheating. I don’t have voltage or coolant temp gauges.
Is there a specific Bluetooth dongle/adapter you use?
I’ve been using this one since 2016.
The cheap Bluetooth ones work as well as the expensive ones