On a related subject, I once dreamed up a non-OTU (or quasi-non-OTU) ATU roughly inspired by the Interstellar Wars and the Ramshackle Empire. In a nutshell, in the late 21st century, Earth has been conquered by the Reticulan Empire and placed under a puppet global government. The Reticulans (AKA 'Greys') then proceeded to heavily exploit Earth's economy, resources and work-force.
In the 23rd century, a bloody revolution swept away the puppet government and established the United Terran Republic (UTR). This, of course, was answered by an intervention attempt by the Empire and its many thralls (as the majority of the Imperial Army were Auxiliaries - troops 'donated' by vassal species) and led to a massive interstellar war. The Terrans, owing to their desperation, thirst for freedom and iron-fisted leadership, as well as the rebellion of several other vassal species against the Empire, won the war. The great - but old and corrupt - Reticulan Empire was forced into a armistice treaty with the UTR, recognizing the Terrans as an independent power and allowing Terran merchants and mercenaries to operate in Imperial space.
Now the Terran upstarts, with their energy and tenacity, rampage across Imperial space. Imperial administrators, unwilling to deal with the cumbersome Legion system, hire Terran mercenaries to fight dirty brush-fire wars for them on the worlds they oversee. Terran smugglers bring new high-tech goods to worlds which were deliberately kept low-tech by the Empire, unravelling their social fabric. so-called Minor Species, liberated by the Terrans during the war, now exist as autonomous polities inside the UTR. Profits and high adventure abound.
(To clarify, the Terrans DO NOT rule the Empire - yet - but are getting entangled in its convolved internal politics, being used by one Reticulan administrator against the other).