Mattermost is an open-source rival to this company's product.  
In an interview with MIT Technology Review, the CEO of this company called its product "just a giant piece of shit. Like, it's just terrible and we should be humiliated that we offer this to the public."  User onboarding guru Samuel Hulick wrote a February 2016 Medium post about how he was "breaking up" with this company's product because it was asking for "A LOT" of his time.  Mattermost is an open-source rival to this company's product.  Ben Thompson has forecasted that this company's Botkit framework will make it the winner of a post-Facebook internet age.  The CEO of this company had earlier co-founded Flickr and is named Stewart Butterfield.  This company grew out of a failed startup called (*) Tiny Speck, which developed a side-scrolling MMO called Glitch.  Similar to IRC, people using this company's service communicate through open channels.  For 10 points, name this company which makes a popular enterprise chat app.
In an interview with MIT Technology Review, the CEO of this company called its product "just a giant piece of shit.
Slack