The program is called Space Simulation Toolkit, you can buy it or try the demo here: https://sstgame.com
Also check out SST discord server:   / discord  

In the last update (which is huge by the way) actual gravitational interactions between particles were added. The possibilities of this game have expanded infinitely... again. This is a 12x timelapse of

some cool flying balls

timestamps:
0:00 - start of the simulation
0:20 - the planets now have distinct boundaries
0:50 - the main ring starts to collapse
1:20 - first collision (a pretty boring one)
1:31 - a series of collisions including one planet crashing into the core
1:40 - some protoplanetary activity

there's a lot of cool stuff happening between these timestamps

3:10 - the last collision. Only accretion will happen after this point