I've worked in several offices around 2013 where people happily used Skype like IRC: everyone was in a list of ~10 channels and occasionally sent private messages to coworkers. Instead of building on this, Microsoft kept pushing its unpopular business chat app (Lync) and made sure that Skype was only useful for consumers (obnoxious birthday notifications, the "snapchat redesign" etc.)

Skype could have beat Slack to the punch. Instead Microsoft lost both the business and the consumer market.