I applied online. The process took 2 weeks. I interviewed at Slack (San Francisco, CA) in Aug 2016
Interview
Extremely fast follow-up to my submission. First is a screening interview and then you are assigned a project. The people there are responsive and nice from my experience. The only bad criticism I have is the lack of feedback for being turned down on my project's performance, but I guess it has to do with a lot of red-tape and what not so it I don't blame the company. I will be applying again due to the simple process.
Interview questions [1]
Question 1
Why Slack? Previous projects you've worked on? Week-long project.