Far (far) better UX and onboarding, and the free tier. I've only worked in one place that payed for Slack. It's easy to underestimate how much UX matters, but

Far (far) better UX and onboarding, and the free tier. I've only worked in one place that payed for Slack. It's easy to underestimate how much UX matters, but it does, as long as the user has a say in the matter. Otherwise we'd all be swimming in Android phones.