I use Slack every day. I have multiple teams I’m connected to, including a personal one that’s dedicated to RSS feeds. The platform is versatile and unusually well designed. It’s probably my favorite app on my Mac.

What’s interesting is that Slack’s tech stack is very traditional. Old school, even. From one of its job pages:

The main tools that we use to build Slack are PHP, MySQL, and Linux – reliable tools that the Slack team knows well and trusts.

At a fundamental level, Slack deliberately seems to avoid sophisticated tools that get in the way more than help. On this same job page:

We are looking for other engineers that understand that simplicity and reliability are aspects of a system that can’t be tacked on but are carefully calculated with every decision made.

Slack’s JavaScript framework seems to be a homespun mixture of jQuery, pure JavaScript, and an in-house plugin called Monkey scroll. One of the critical requirements of its application engineer position is that you should be comfortable with functional programming languages “used without frameworks.”

It’s ironic that the de facto demo app that shiny modern tools show off to prove their viability is an instant messaging app, but that the number one app for business messaging, Slack, is built of tools that are much older.