The one in the WordPress repository is made by a guy named Donncha and it works very well in my opinion as does our own but ours is a little more strict in the types of domains it will resolve.

The one in the repository will resolve a sub domain to another sub domain where ours normally does not work well for this previous example, but then again ours works great for mapping TLD's to sub domains.

There are also other integrations with other plugins that ours works well for and I do not know if Donncha's works at all i.e. Multi Domains plugin

Is this functionality built into WP already without the need of a plugin at all?

No there is not.

Cheers, Joe

It actually looks identical to the WPMUDev domain mapping plugin. Are these actually the same or what is the difference? Is this functionality built into WP already without the need of a plugin at all? Thanks for shedding any light on this.