Disclosure: I work there and have written articles for the blog.

At the moment we mainly blog about our experiences with Golang (our language of choice right now). But really it's open to any topic someone in our engineering team is interested in writing about.

We aim to keep things visual, interactive and example-based. For example Jim Fisher created an interactive animation of Golang's GC algorithm here: https://making.pusher.com/golangs-real-time-gc-in-theory-and.... We also managed to embed Golang's trace visualiser within one of the posts: https://making.pusher.com/go-tool-trace/#tour-of-the-go-tool... (using some pretty dirty tricks).