In the grand tradition (opens in new tab) of releasing a new thing for a game just as we're beginning to forget all about it, iD software have bolted the official toolkit for Rage (opens in new tab) onto Steam. You can finally build your own environments, guns, mutants, cars or whatever else. Perhaps you could swap John Goodman's character Dan Hagar for one that looks more like John Goodman, or create a mod that changes the colour palette from 'very brown' to 'less very brown' - whatever your heart desires. However, there are a couple of things to bear in mind with the download, not least the fact that it's a whopping 35+ GB in size.
There's a welcome document (opens in new tab) accompanying the toolkit, which makes clear that the kit is "provided on an 'as is' basis only for the technically sophisticated and adventurous." iD's John Carmack tweets (opens in new tab) that "The toolkit release is not something that we consider consumer friendly, but it does let you get a look inside the construction process."
To download the toolkit, head to Tools section on Steam (it's helpfully listed as Rage Tool Kit).
Thanks, Eurogamer (opens in new tab) .