A nice feature on most models prior to the Clara HD is an internal uSD card. (This is different from the externally accessible uSD slot found on some models.) Pop open the case, remove the card, make an image, and you can be assured of restoring it to a working state without any fancy tools. With the uSD card in a computer, you can examine it and modify it. The models that I have cracked open also have a place to add a header for a serial connection, though I haven't tried using it.
Kobo does not appear to have any interest in locking down their devices. Software updates are shipped as zip compressed files wrapping a gzipped tarball. That tarball is simply a directory tree containing files to add or replace. Many third-party modifications are distributed in this manner and you can do your own modifications without ever cracking the case open. (Though I do suggest opening it up and making a backup before modifying it.) As far as I know, there is no protection on the proprietary software components and Kobo hasn't said anything about third-party patches. This has been the case for nearly a decade now, which is why I lean more heavily on the word modifications rather than hacks. Most of what can be done relies upon an developer's knowledge of Linux.
There are also various projects that you can learn from. Some provide tools to make developing software for the Kobo easier, while you can examine others to figure out how to setup a toolchain. I have seen C, Rust, Lua, and Python based projects for Kobo readers.
The Kobo development forum on the Mobileread forums is the place to check out for more in depth information.
I don't know what's involved with trying to do the same thing with Kindles, and I don't know about hacking the firmware.
Which (as far as I remember) doesn't include epub, the ebook format.
> I don't know what's involved with trying to do the same thing with Kindles
Kindles behave in the exact manner you just described. There is no difference. (Well, the Kindle won't read an .epub. They read .mobi instead.)
Cheaper than most other e-readers for what you get. Fully unlocked and ready for you to SSH into.
Lively, polite, and active hacker community.
Any (perhaps subsidised) alternatives that I can jailbreak?
The software running on both devices is identical. The main difference from my understanding is that the battery life is better on the RM2, and then pen has an eraser on the back.
I've heard mixed results about writing quality, from my reading most people have said writing on the RM1 "feels" better.
The next model is planned to use the Raspberry Pi Pico microcontroller https://twitter.com/josecastillo/status/1356125145681846276
https://old.reddit.com/r/Onyx_Boox/comments/hk7d5v/onyx_is_v...
Here is an exmaple of a Bash-based extension for the Kobo, which downloads files from cloud providers for you: https://github.com/fsantini/KoboCloud
And here is a forum with lots of people sharing tips and mods for it: https://www.mobileread.com/