Geth VI

The Geth VI is a network of geth virtual intelligences created by the "true" geth to study the Reapers. If Legion was sold to Cerberus or was never activated, it is first encountered during the mission to disable a geth dreadnought. The Geth VI also accompanies Commander Shepard into the geth server and provides support during the assault on the Reaper base on Rannoch.
If Legion became part of Shepard's team but did not survive the suicide mission, Tali (if she is present on the geth dreadnought) refers to the VI as a "backup" of Legion, comparing it to how her people had once been known to create virtual reconstructions of dead individuals.