Found this website that looked like an archive of someone's work; it was essentially an encyclopedia, organized in chronological order, of transhuman "species" as they developed. It takes a twisted turn when the solar system is invaded, and the aliens further bioengineer (to the point of unrecognizability) these populations, sometimes for pragmatic reasons (using humans as tools,) to engineer pets and vanity creatures, and some out of sheer spite-- one population is transformed into a living mat that covers the floor of a sanitation system, turning them into a self-aware sewage treatment system.
Most of the populations are no longer sapient, the intelligence cut out of them. There might have been a second alien invasion described later in the entries as well. There are no protagonists, and there's a good chance the "story" covers millenia? I only skimmed it the first time I read it, but there were some interesting ideas.
PS: the whole thing was illustrated. disturbingly illustrated. To expand on this, the illustration looked like woodcuts, and the figures depicted were usually naked and grotesque, with features so exagerated it bordered on charicature.
The site itself looked old (basic html webpages?) even though I had found it only in the last couple years. It's very possible the site was webarchive of a published book, but I can't be sure.
Other species may have included:
Venusian flyers capable of staying afloat above the planet's oppressive atmosphere.
More to come if I can think of them.