I accidentally became the owner of 9 old HP Pro 3400s. Help me not turn my living room into a data center (or at least let's have fun doing it!)

So I got a lot of 9 (nine!) HP Pro 3400 desktops. Each one comes with: Pentium G630 (2 cores, 2.7 GHz) 4 GB DDR3 500 GB HDD, all tested and healthy Keyboard, mouse, 24' monitor. All nine boot. My electricity bill is already nervous. I already run a NAS with truenas on a Fujitsu i5-7400, and I was thinking about moving the apps I currently host on truenas (immich, ...) on a Toshiba Satellite PRO C660-2LP, so I'm not starting from zero, but I have no idea what to do with this many tiny space heaters. I'm looking for: Fun, useful or weird projects that make good use of one or more of those computers Ideas for reselling/gifting them without losing my mind (bundles? linux+custom software? who actually buys these?) I'm keeping one or two for backup/replication duty, but the rest need a purpose or a new home. What would you do with 9 identical, underpowered, slightly smug office PCs?