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What Amazon Kindle? Here's an Open Source eBook Reader
(itsfoss.com)
This is a most excellent place for technology news and articles.
It's a raspberry pi pico. Ebooks could probably work with it on the new version.
It said it's a 120mhz SAMD51 ARM Cortex-M4.
There's a version with the pi pico https://github.com/joeycastillo/The-Open-Book