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 running one with a dozen or more users on bare metal at home for the last two years. A little bit of spam but otherwise fine. No deliverability issues or anything.