KOReader: Open-Source eBook Reader

Absolutely love KOReader. I use it on my Kindle 3 and have moved my parents and brother over to using it on their Kindles as well. You can even install it on relatively new models thanks to the recent WinterBreak gaolbreak.

There was some discussion about it on HN not long ago:

All Kindles can now be jailbroken | 1377 points by lumerina | 2025/02/17 | https://news.ycombinator.com/item?id=43073969

I found KOReader's Android app a tad buggy, but the experience is wonderful on Kindles. If you've got an old Kindle kicking around, I also wrote up a little thing about bringing them up to speed which mentions KOReader: https://vale.rocks/posts/improving-early-kindles

Same experience on a PaperWhite 2, been using it for a long time.

It is a good reason to look into rooting, PDF reflow and the function to remove margins make it possible (at least tolerable) to read PDFs when an .epub / .mobi is not available.

You can also run Alpine Linux on a rooted Kindle with graphical interface, I found it amazing but ultimately not that useful with the limited system memory.

PDF reflow is one of the major reasons I am using Koreader. The whole thing is very clever and works extremely fast given the limited nature of these devices.