InkBox OS – open-source, fully-functional standalone OS for Kobo's eReaders
inkbox.ddns.net
inkbox.ddns.net
Last time I was at Value Village I saw a handful of them for $5 each. I picked up a couple of them and turned one into a weather station[0]. Took under 5 minutes including mounting it.
It's not all open source though. They will give you access to the device and you can fairly easily move files on and off, but the app is proprietary.
Being able to strip the DRM so I can read on non-Kindle devices is a major cat and mouse game and it's majorly frustrating to have a solution worked out only to have it break the next time I buy a book. Has anybody had continuing success with this?
Technically it's not really a firmware replacement, but an application on top of it (implementing pretty much all e-book related features).
There's even an Android version, which is how I use it on my Boox tablet.