InkBox OS is an open-source, fully-functional standalone OS for Rakuten Kobo's eReaders.

InkBox OS

Here are some of InkBox OS' features:

Fully integrated KoBox X11 subsystem
ePUB, PDF, picture and plain text display support
Versatile configuration options for reading
muPDF rendering engine for ePUBs and PDFs
Wi-Fi support and web browser
Encrypted storage with EncFS
Fast dictionary & local storage search
Dark mode
Full factory reset option if needed
Seamless update process
VNC viewer app
Search function
10 built-in fonts
Lock screen/passcode
User-friendly experience