I had a species called the Merkhut in the Delta Quad that was a Terran seed ship that fell through a wormhole, composed of undocumented Augments that erased thier records and blasted off from earth during the final days of the Eugenics war. They found several low tech planets, 'assimilated' the population and began crash building up a society and fleet to expand.
They ran into several alien races, harvesting them for genetic resources they thought would prove useful (telepathy, improved physique, etc), and began expanding outward.
Then came the Borg
Through a quirk of genetics, psychology, luck, tactics and sheer ruthlessness, they have managed to survive for a significant period of time against the borg, prefering sucicide tactics and system killing weapons to wipe out Borg invasions. The Borg for thier part, finally decided that it wasn't worth the resources expended to assimilate the species as the ammount of drones lost vs captured merkhut made it a losing proposition and evenutally relented for softer targets, occasionally sending the occasional cube back to test defenses.
Bad idea. The Merkhut had been busy adapting borg technology, taming it, and making countermeasures against Borg assimilation systems as well as listening to the hive through it's own subspace network, adapting as it went. They have the distinction of being the only species aside from Humanity that hasn't fallen to the Borg.
But they've become much like the Borg, developing a telepathic 'hive mind' to draw the 'collective' merkhut knowledge from. They do not tend to think much of individualism (which leads to certain psychological flaws), are blunt, direct, and completely ruthless in dealing with thier enemies.
Then they noticed that a tendril of the Borg Collective went silent in the alpha quadrant. Puzzlement mixed with curiosity had them build a transwarp network into the Alpha Quadrant and send a vessel to seek out what had happened and determine if an alliance verses the Borg and other species could be attained. A vague racial memory of coming from the Alpha quadrant stirred and when they met with the Federation, some awkward moments ensued when the terrans found out they were decended from Augments (the taboo against genetic modification failed to register with them).
They've been an interesting NPC species in the background, tho species isa relative term as they grow various sports of mixed alien DNA and genetic constructs to tailor an individual for a needed task, al the while making them genetically adapatable. More of a frame of mind than anything else.
Perhaps I'll do a write up fo them when I done with the module I'm working on
A brave little theory, and actually quite coherent for a system of five or seven dimensions -- if only we lived in one.
Academician Prokhor Zakharov, "Now We Are Alone"