Lookit, I love Slack. Used it extensively in a huge team.
But I do get tired of the constant thing around HN whenever a company releases some new feature, people immediately post a "Well, credit should really go to XYZ who did it first".
Sometimes the other company did launch a similar feature first, sometimes the features aren't that similar, and more often than not, everyone is copying from everyone. (and that's ok)
If you're not being sarcastic... well, I think Shank summed it up pretty well.