Chia cryptocurrency. My dad got into it, and the price was mooning. Gave me an excuse to build a new PC and learn linux, so I thought it was a worthwhile investment. Sunk a decent chunk of change into hard drives that I still have laying around, but I’m using several of them and have a sweet gaming rig that I would’ve built eventually anyway and had something to talk to my dad about. So basically, just out the cost of some drives. All in all, it was a calculated risk that didn’t pay off.