I can recommend ViMusic. I got it from the F-Droid Store. It basically get's every song from youtube, with a very nice gui. Not a song i didn't find yet.
I am using a Tolino Vision 6 and I am very happy with it. No cracking or modding neccessary. All my ebooks are synced with Calibre, it recognizes the device without a problem. I wouldn't want to support amazon if I can avoid it.
Free ebooks at my town: borrow an ebook at the local library and convert it with https://www.acsmconverter.com/ from the .acsm format to epub. Although it doesn't work all the time..
If anyone knows a more reliable way to convert from acsm, please let me know.
Awesome, that you develop tools for lemmy! Thank you.
A question: Did you consider to publish your app on the F-Droid-Store? I only use apps from there and the only usable app for lemmy is jerboa. An alternative to that would be awesome, as it has quite a lot of problems.
Here comes the least helpful answer: Give Linux a try.