Parallel Trouble Adventure デュアル! ぱられルンルン物語

From the introduction:

Have you ever wondered how much one small decision could affect the course of history? Well while this might be an example on the more extreme end of the scale, one choice is how it all split apart.

22 years ago, a huge alien artefact is found on a construction site and (unknowing of its alien nature) the foreman orders it to be destroyed. Here is where the world splits into two. In one world, let’s call it world A, the worker who examined the artefact tosses away the small piece he picked up and the artifact is destroyed. In the other, world B, the worker keeps the artifact, presumably taking it to be examined and leading to the discovery of alien technology that changes the world.