Transit reader (and book maker)
In April, I got myself an X4 and installed CrossPoint on it. It is a combination that embodies the spirit of open-source; no lock-in, no rent-seeking. Driven by buttons, I like reading on it during my commute; and I am already on my second book.
X4 charges via a USB-C port, and takes a microSD card for storage. Adding books and reports is easy as putting files (books, reports, text, even custom fonts and wallpapers) onto the card.1 It reads ePub like a native, and unlike a Kindle, no file conversion is necessary.
To produce books or reports as ePubs, have a look at Pandoc book template. It takes Markdown files, some metadata, optionally cover image, and other book related artefacts.