Not entirely passive, but I'm a Nominet registrar and buy/sell domains as my side gig. For the most part, this involves taking preorders for domains which have

Not entirely passive, but I'm a Nominet registrar and buy/sell domains as my side gig. For the most part, this involves taking preorders for domains which have expired and are about to drop, then trying to catch them when they do. I also hold my own domain portfolio which currently consists of just over 200 domains. I generally have an idea for how to develop most of these, but I'm mostly just holding them until I get time to work on them. Depending on what's dropping, my earnings from the domain side can vary drastically. It usually covers its own costs, and my best month so far (I only started in April this year) earned me around £1000