[optimusclimb]

This always comes up with Martin Kleppman diagrams. See this discussion:

https://news.ycombinator.com/item?id=9613118

The bottom comments seem to agree it was done using Paper.

[twic]

From the Kleppmann's mouth:

https://twitter.com/martinkl/status/629169643710775296

I saw him talk at a conference, and that was one of the questions someone asked. He must be so fed up with it by now!