It's almost all economies of scale and "rich get richer" type effects, much like the big social networks. You make something that catches on (in Slack's case it

It's almost all economies of scale and "rich get richer" type effects, much like the big social networks. You make something that catches on (in Slack's case it really did have an edge on the existing stuff) and from then on you've got your loyal user base for whom it would be too much of a project to move to another thing. Slack is a great product, but at the end of the day it's a mildly more convenient way of doing stuff that you could do in 2002 with IRC and email. And Mattermost is a pretty good FOSS substitute. (This isn't counting audio and video calls, but those have been pretty good since around the time of Google Hangouts, long before Slack had audio/video.)