Screwed around with this game a while ago, but it seems to have exploded in popularity more recently.

I don't pay for it, and actually haven't looked at it since, but I did find some O_O videos of what people have made in it:

Rollercoaster:
Source: YouTube


Earth model:
Source: YouTube


Notre Dame:
Source: YouTube


16-bit ALU: (an Arithmetic Logic Unit is like the brains of a CPU)
Source: YouTube


Star Trek Enterprise Ship:
Source: YouTube


Some people really do have too much time on their hands...