My 2011 iPad 3rd gen.
A lightweight Linux distribution would make that thing killer for word processing and document reading. Might even allow YouTube videos to be watched again.
Any equivalent Android tablet would have custom ROMs etc. to get a bit more functionality out of it. I know it’s not a tablet, but look at the Samsung galaxy SII - the amount of community development for that is incredible to this day.
I’ve been daily driving a Lenovo X230 tablet for the last four years. I use Xournal++ to take notes with the pen in classes and at work. Works great!