The "lesser Homeworlds" were a secret expansion of the Nine Homeworlds project initiated by Oldblood Great Houses in response to House Military's embracing of Newblood tactics. The "lesser Homeworlds" were kept in bottle universes and oxbow timelines to fight microscopic models of the War in Heaven with far less scope or intensity. Their purpose was to provide inspiration for technologies and tactics.
One collection of "lesser Homeworlds", which the post-War edition of the Primer for the Spiral Politic described as "notable in hindsight", fought against a race of mechanical invaders who had agreed to fight them in exchange for time travel technology, (PROSE: A Prelude to a Prelude) having allied with the Houses in the face of the All-High Gods. (PROSE: Dead Romance) The Sixth Doctor once found himself in another universe where the Time Lords fought a simplified War in Heaven against the Daleks which ended in the universe being destroyed. (PROSE: The Quantum Archangel) The only "lesser Homeworld" to survive War against these machine-people did so by abandoning looms and returning to organic models of birth, allowing it to enact the victimhood ritual of an entrenched last stand by crying out to future, "Won't someone think of the children!" (PROSE: A Prelude to a Prelude) A similar survival occurred on the last day of the Last Great Time War. (TV: The Day of the Doctor)
The "lesser Homeworlds" project was discontinued when the number of lost Homeworlds became "too distateful to bear". (PROSE: A Prelude to a Prelude) Entarodora once alluded to these losses in a lecture: "While it is true that we have lost more Homeworlds than might be thought prudent it must be remembered that many of these were essentially decoys, and their people mere sheath-echoes of our own core probability." (PROSE: The Brakespeare Voyage)
Behind the scenes[]
The collection of lesser homeworlds which were "notable in hindsight" was one of many attempts to incorporate the Last Great Time War into the Faction Paradox mythos. This attempt was intended to imply that the Gallifrey of post-2005 Doctor Who, or at least the one shown in TV:The Day of the Doctor, wasn't the original Gallifrey, but instead one of its many cloneworlds, an idea some fans had already speculated.