Their base product is bringing in $5/month/user, and they'll often get dozens to hundreds to thousands of users for each company that joins, whose employees are usually already using the free version of slack, as a sort of grassroots movement within companies. It's been the primary means of asynchronous communication for the last ~5 customers I've worked at, and I've been in slack channels of 30 to 300 users - in total, an easy 500 paid accounts, and that's just from my network.

Anyway yeah it's a risky investment and a precarious valuation, there is plenty of competition out there right now, yet somehow nothing seems to be able to come out as better than Slack. Maybe if a party actually spent those millions in investment funds to create good non-Electron apps.

Tool integration and automation with Slack are things that people have come to depend on. There’s not much unique to Slack in that regard but they have the momentum and many products will either be Slack-first or be integrated exclusively with Slack. There’s a lot more out there in terms of APIs these days so people can, and do, develop their own integrations for other chat platforms but that’s not quite the same.

I don’t know about 7 billion but based on how technical and non-technical teams alike use and depend on Slack I can easily see 1 Billion or more. But 1 and 7 billion are really far apart. If I were a Slack employee I’d be thinking about my stock. If it sold for 2 billion would I be shit out of luck? Legitimately asking, I don’t know how stock preference works when the VC investment comes after stock has been issued to an employee.

Because their value isn't from the product itself. It's from being able to dig into the data being transferred with the product.

They have a deal with Corsair and Micron.

Because lots of companies pay for it.

Have you been living in a cave for the last decade? This is modern business, whatever is hot and gets a lot of users, gets a ridiculously unrealistically high valuation. Also, you never need to be profitable, as long us ure hot you can just keep doing more rounds of funding.