I've started an Oanakli trader collective (from Octavia Butler's Exogenesis books).
For those who haven't read the trilogy, the premise is that humanity wipes itself out and this alien race, the Oanakli sweep in at the last minute (they were watching, unsure if they were witnessing the accidental self-destruction of humanity and so should interfere, or a purposeful suicide, and so should not). They are peaceful vegetarians who love life, look like creepy anemone people and have three sexes, and hypersensitive tentacle/stingers which lets them read precise genetic information from everything. The third sex is the Ooloi who have extra tentacle arms that let them manipulate genes directly, up to building viable lifeforms in their own bodies for hatching or planting.
To the Oankali humanity is intrinsically fucked: we are both intelligent and hierarchical, which to them is stupid and unsustainable, but also really exciting, in a "self-destructive anti-hero/sexy badboy" way. On a genetic level.
They rescue everyone they can, put them into hibernation, feed what they can of human civilization (cities, etc) into their shuttles, let earth grow over with jungles, let radiation fade and wake people up to explain what they want from us. What they want is our genes, especially cancer (which they can use to learn to shape-shift and regenerate), and in exchange they'll fix us, but also make us into them (sort of), in the sense that we will grow tentacles, and completely revise our entire sexuality around the ooloi third gender, and its' crazy gene/sex/addictive chemical/hallucination powers, which in turn will fix the whole hierarchical issue vs. intelligent issue.
Also its isn't really an option to say no. Welcome to Oankali trading!
so Natural sociologists, Adaptable, Deviants, Slow breeders, Prole species, and a serious beeline for genetic manipulation and the related culture project.
Along the way I "traded" with a medieval race of floating, militaristic and very strong plants (slow breeders), a race of intelligent, but fragile squid people. A race of subterranean, adorably cute mushroom people who were also natural physicists (sedentary), tunnleled up in my second world and occasionally produced refugees. My prole race were many-armed lizards. Between these and my generous openness to immigrants (mostly horse and squid people from nearby peaceful civlizations), my Ooloi had plenty of room to experiment and my biology research was off-the-charts.
Soon I hit the point where I could manipulate genes directly. I started with the lesser species. We aren't building one super races, we are building 7. Already my president is Ooloi floating gourd from a world which was having medieval wars just a decade before.