Brilliant.org is shutting down community section to focus on interactive courses

It's really disappointing to see this happen—especially from a website / community that is so widely advertised on sites like YouTube.

Although I understand their struggle to support their community section given their limitations, it seems as though this change is less focused on the satisfaction of the users of the site (despite their claims otherwise) and more focused on increasing revenue.

Does anybody have any recommendations for alternative communities that focus on a similar area of interests? I personally enjoy the challenges of Project Euler, though that doesn't quite fulfill the same role as Brilliant's community did. I'm always on the lookout for new and interesting ways to learn more!