Like many technologists, blockchain technology starting with Bitcoin has been fascinating. I spent my share of 2017-2018 participating in speculation alongside tech coworkers, though only with money I was willing to lose (and I did lose most of it). I watched most of Tim Roughgarden's lectures about the math and theory behind blockchain, much of which was a repeat of my Computer Science masters degree coursework in distributed systems. I've also explored making my own smart contracts, learning a lot from this excellent video.