We initially used Skype on our team to communicate with others. However, the software was horribly buggy on OSX. Slack has become part of our main toolchain. It works, has the basic features you need and doesn't get in our way. The integrations are great and we'll continue to use them. Unless Microsoft rebuilds Skype for the ground up, I don't see us leaving Slack for it. They had their chance, and they dropped the b…
Microsoft had their chance and dropped the ball on a lot of things, but they always figure it out. Skype on OSX looks much better now and I suspect if they're focusing on Skype instead of spending $8B, then you're looking at serious competition.
Plus, I would never use it professionally since Skype (and MS in general) are the extreme low in regards to privacy.