I am pondering a world, where life very early on took a slightly different turn. First some background sketch, to explain what I mean:
Current theories state that life first evolved as protocells: little pores or similar, in which certain chemicals got concentrated and electro-chemical potentials could build up in a natural way; later on, primitive, single celled organisms, like bacteria and archaea arose, which could live independently of thise environment. At some point an archaeon somehow engulfed a bacterium and learned to live with it; the bacterium became the mitochondrion, and the result was the eukaryotic cell, which over time evolves into us, among other things.
Bacteria and archaea have at an early stage evolved to form biofilms; to do this they have had to learn to cooperate and communicate, in some primitive sense, by means of chemicals and electric signals (they do this even in our reality) - and they exchange bits of DNA. Imagine now, that instead of eukaryotes arising, these biofilms evolved ever higher complexity, specialisation and organisation, so that they in effect became multicellular lifeforms, but consisting of large numbers of different species of bacteria and archaea.
What would they be like? Could they evolve intelligence? And what would happen if they one day learned interstellar travel and came across these bizarre monocultures called humans?