Slack uses PHP for most of its server-side application logic, which is an unusual choice these days. Why did we choose to build a new project in this language? Should you?
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PHP-the-language has many flaws, which undoubtedly have slowed these efforts down, but PHP-the-environment has virtues which more than compensate for those flaws. And the options for improving on PHP’s language-level flaws are pretty impressive. On the balance, PHP provides better support for building, changing, and operating a successful project than competing environments. I would start a new project in PHP today, with a reservation or two, but zero apologies.by Keith Adams, Slack Engineering
Source: Taking PHP Seriously
Rather interesting to learn that the server side of Slack is written in PHP. I guess I assumed it was a Ruby or Go thing. I think it’s useful to hear about success stories for a mature language like PHP. It shows us that just because something has been around for awhile doesn’t mean it can’t do something cool.