The cap has plastic. The glass is sharp and dangerous for a while each time it cracks. It is trash and should not be put in the sea. This news will spark just a bit more pollution.
Fabularium (the F-droid version is bit enhanced over the original). It is an engine to play text adventure games like Anchorhead or Zork. Get the games at ifdb.
You should see a link inside obtainium itself, when you press "add app". Just press on "crowdsourced..."
The programs listed there are the harder ones to setup correctly for obtainium, so you should primarily use that, and if the app isn't there, then paste the github link / fdroid link / etc like you would normally in add app.
Raspberry Pi I'm not sure if it's worth it. But in short you can advance some science with spare CPU hours. Should be possible to limit it so it doesn't heat up and use just a bit of the cycles depending on other load...
It's great, can revommend!