The article on TidBITS says OmniFocus 3 requires macOS 10.12+ but Omni Group’s website says it requires 10.13. I really wish TidBITS was right and Omni Group was wrong, but I kinda doubt it. My Macs are still on 10.12. I didn’t see any compelling reason to update to High Sierra and I’m still not quite ready for Mojave. But being able to run OmniFocus will be a big motivation to bite the bullet and install 10.14.