While having Rock Simulator playing, press Ctrl+Alt+Del to go to the lock menu. There, select "Task Manager".
You'll have access to the taskbar, to which you can click on anything there and do whatever else you want.

• Work on something else.
  
• Watch videos on the internet.
  
• Binge scroll on your usual social media website.
  
• Eat.
  
• Sleep.
  
• Chores.
  
• Go to your actual part-time job.
  
• Touch grass.
  
• Visit your parents.
  
• Do that one thing you keep forgetting to do.
  
• Contemplate on the actions and decisions you've made throughout your life.
  
• Act like an actual rock.
  
• Play something else?
  
• Eh, whatever.