FOSS Oriented E-Readers?

I love the hardware of devices like Kindles or Nooks etc. However, these are all closed gardens. I dont own the software. And with devices like the Kindle they now come always connected to the internet with a LTE connecting owned by Amazon and lock you into their ecosystem of ebooks. Is there any hardware out there that fulfills the design of an e-reader but doesnt lock you into their walled software garden? The closest thing I could think of would be just a normal android tablet with an e-ink display but I doubt any that exist are of good quality or could even allow me to put my own software on them.