fread.ink is a free as in freedom alternate operating system for electronic paper ebook readers.
fread is currently under development and not yet ready for normal use. I am aiming to launch a version 0.1 for developers in early 2018 with basic support for at least 4th generation Kindle touch and non-touch.
The plan is to support the most popular e-readers with electronic paper displays starting with i.MX5 and i.MX6 devices, which surprisingly covers most of the widely sold models including all Kindles since the 4th generation (2011), every Kobo since the Kobo touch (2011) and the latest Nooks (since 2016). The older Kobos and Kindles that use older i.MX chipsets will likely be supported at some point. For older Nooks I haven't sufficiently investigated the available source code to know whether support is feasible.
Developers should start here. Assuming you own a Kindle 4th generation non-touch and have root access then this should get you as far as booting into a modified Debian Jessie with basic graphics support.
Status as of March 5th 2018: USB networking is working. Button input is working but not for the five-way controller buttons and automatic display updates are sorta kinda working. Here's a little video demo showing an unmodified xterm using fast auto-updates but with the crappy built-in waveform. The waveform format converter is working but has not yet been integrated into the system. WiFi is almost working (but requires a binary firmware blob). No ebook reader app is included and USB storage mode is not yet working.