Or say, take something like the Linux kernel -- that is something very big, very complex, that contains input and work from many contributors. Then take Android an OS, with a VM, with applications running on it all on top of a Linux kernel. If looking at it from bottom up (from hardware up to the highest level application code), that's a lot of system, and subsystems, APIs, ideas and protocols working together. It is a very complex machine it is just not physical and tangible but that doesn't mean it is less complex.