I looked it up (on Google of course) and it seems like this is one of Google's recruitment channels.

You get access to a terminal and a text editor:

Here are the commands you can execute:

You have a week to complete each challenge. I've done 2 of them so far, and requested the third one - they have been very enjoyable and I've already learnt a lot from them.

I'm pretty sure I have literally zero chance of being hired by Google (and I'm not even sure I would want to work for them even if they made the mistake of wanting to hire me), but this has been super interesting so far. And yeah, also a huge time waster, I've been thinking about making the solution to the third challenge more elegant and performant all day instead of doing my actual job.