Most trivial? Not by a long shot. What about WINVER?
Not windows, but `true` has to take the cake for the most trivial program, the portion of my comment after the second : is a valid implementation:
GO.COM for CP/M and DOS was similarly trivial. A 0-byte program, the effect of which was to cause the previously run program (which was still in memory at 0100h) to start again.
Is true a program? I thought it was a command built into the shell.
Most shells optimize it to avoid the overhead of spawning a process for something as trivial as that. But yes, it's an actual binary even so, just in case - try `which true`.