Here's another powder simulation, https://powdertoy.co.uk/. This one still has an active community and development team, and people have built all kinds of cool things with it like actual computers that can be programmed with assembly.
The aforementioned sandspiel is excellent, along with orb.farm (by the same author), and (shameless plug) my own entry in the genre: https://github.com/JMS55/sandbox
