The funny thing is that, unlike fake UI in other movies, this was indeed a real demo for silicon graphics computers: http://www.sgistuff.net/funstuff/hollywood/jpark.html
Towards the end of the movie the kids use the computer to lock the doors. This is the great moment of fsn ("fusion") the File System Navigator which is a real demo application and was not written for the movie. A binary was available from the official Silicon Graphics website for a long time.