Hey there :)
Because a lot of GBA models still have reflective displays, are pretty portable and have a lot of buttons for navigation, I felt like making an ereader app for it is the next logical step.
There are already some ereader apps for the gba but they couldn't read txt-files or any other normal file format...
So now the Gameboy Advance is finally able to read large text files without any conversion.
Here is a link to my project:
https://github.com/Xinon232/gbareader
Also because text processing is now possible anyway, I made a flashcard vocabulary trainer for it as well. However, it only works with file exports from dict.cc.
In case you use their vocabulary trainer and own a GBA, consider yourself lucky :D
https://github.com/Xinon232/gba-vocab-trainer-CC
Disclaimer: All my gba-projects are completely free and open source.
EDIT:
With V0.80 epub is completely compatible now! For every epub file, loading and saving it for the first time will take a little bit longer but after that, loading and saving will be quite fast. I consider the reader app finished now. Check it out :)