Unity

The Unity was the name of Richard Grey's vision of humanity after the war. In order to avoid the self destruction of the species, he desired to forcefully evolve humans into one, perfect race, removing the inequalities that are the cause of strife among humans. To this end, he used the Forced Evolutionary Virus to create his race, the supermutants. However, according to his Audio Log, he also had a different vision, one that involved merging humanity together. Literally. It is possible that the discrepancy is due to the Master having multiple personalities at this point, each which different ideas of what the future of humanity should be.

With the discovery of the Los Angeles Vault, and the establishment of the Children of the Cathedral, the Master created the means of conversion and recruitment of people into his project. Under the disguise of apostles of peace, establishing hospitals and churches in the cities of the wasteland, the Children and the Nightkin prepared for a war that would change the face of the Earth and bring upon the master's dream.

However, the Unity was destroyed before it could be created, by the Vault Dweller, who killed the Master and destroyed his research center as well as the Mariposa Military Base, destroying any chance of the project ever succeeding. Regardless, even if the Master DID succeed, the Unity would fail, as the FEV rendered the supermutants sterile and the Unity would bring about the final end of humanity.

As for the Master's followers, the super mutants split into several different groups. A very large group traveled East, reaching as far as Chicago, another group was noted in a converstation from Fallout 2 as traveling North, some (like Marcus) settled down to coexist with humans, and some small groups still wander the wastes attacking all non-supermutants. If the Fallout: Brotherhood of Steel console game is taken as canon, then another group led by Addis traveled to a secret Vault-Tec Vault but were destroyed.