I first got the Alpha 8 build for Windows 7 somewhere around late-2013 to early-2014, and I ran that pretty continuously all the way up until the end of 2015. I then got Alpha 9, which I used to run more up-to-date builds of the default buildings, while still using Alpha 8 for my custom buildings. I then kinda took a year's break from Skyscrapersim for the whole of 2016, mainly because the laptop I was running it on had just been upgraded to Windows 10 and its CPU speed had dropped significantly with the upgrade. In 2017 I went back to running Alpha 8 and 9, and then towards the end of 2017 the laptop began to perish. At that time, I installed the latest MacOS dev build on this current MacBook that I'm using right now, and I've used that from 2017 to present. There was my very long-winded way of saying "since 2013-2014" XD