Earlier quoted context omitted.
> We even started building and maintaining our own chat app God I love the Not Invented Here disease. Somebody, somewhere, thought "hey, slack is way to expensive, we don't want to get 'locked in', and 'mumble mumble privacy cloud evil stallman' so lets write our own chat application.... how hard can it be?" Boom, now the company is straddled by a shitty, homebrew chat application that is maintained by nobody because…
"Enterprise" slack is $15 per head per month. This would equate to an recurring annual expenditure of nearly $4.86million for Uber's 27000 employees. Given that Slack can be seen as IRC with some pretty decoration glued up to an Elasticsearch instance, and that Uber already has a highly trained tech org in place, if it wants to make a Slack "clone" for less than, say, $25million (cost of Slack to Uber for 5 years), i…
Anyway, as another commenter pointed out, on an enterprise scale I'm sure you can get a good deal. I can also imagine however that at that scale you'll want multiple Slack servers / instances - which would add cost given how slack charges per person, per server.
So there's a few alternatives then; self-hosted (some parties will offer enterprise customers the option to host an instance of their application on the customers' internal hardware), or rebuild it yourself. The latter one however takes a bit of math - how much is it going to cost to build, maintain and run it? It's easily underestimated.
And yet, it's also easy for people working in an engineering culture with nearly limitless engineering capacity to just build it themselves - motivations being "how hard can it be", and "I need something more challenging than tweaking this button for my employer to earn 0.1% more money on this particular feature". I've seen it happen far too often.