According to Steve Mann: Collaborative reality is both “a shared reality” and a “collaborative mediated reality: a negotiation between two parties allowing one to temporarily access the viewpoint of another”.
One example of a collaborative reality can be seen in the supermarket: in this instance, one might walk around in the store looking for groceries. In collaborative reality, his wife at home can see what he’s seeing and can help him choose the right product. If his heads up display has object recognition and filtering turned on, he and his wife can choose the products they like and and block out the ones they do not. Under this system of “Diminished Reality” all inconsequential products are filtered out, making the shopping experience an easier and more feasible experience for all.
Shared Environment Maps – Writing onto another’s viewpoint – Steve Mann’s WearCam
Another feature of Steve Mann’s tetherless computer-mediated reality system was that the wearer could “choose to allow others to alter his or her visual perception of reality over an Internet connected wireless communications channel.”
An example of such a shared environment map appears in Figure 18. According to Mann, this shared environment map not only allowed others “to vicariously experience our point of view (e.g. here a spouse can see that the wearer is at the bank, and send a reminder to check on the status of a loan, or pay a forgotten bill),” but also allowed the wearer to enable “the distant spouse to mediate the perception of reality.” Such mediation, Mann explains, “may range from simple annotation of objects in the `reality stream’, to completely altering the perception of reality.”
Figure 18: Shared environment maps are one obvious application of WearComp. Images transmitted from the author’s `Wearable Wireless Webcam” may be seamlessly “stitched together onto a WWW page so that others can see a first-person-perspective point of view, as if looking over the author’s shoulder. However, because the communication is bidirectional, others can send communicate with the wearer by altering the visual perception of reality. This might, for example, allow one to recognize people one has never met before. Thus personal imaging allows the individual to go beyond a cyranic  experience, toward a more symbiotic relation to a networked collective humanistic intelligence within a mediated reality environment . (C) Steve Mann, 1995.
With the advent of consumer-grade heads up displays, diminished and collaborative reality will finally be possible. What kinds of applications will it be used for? I can imagine collaborative shopping for friends in different cities, vicariously watching or touring a country through the eyes of another, and real-time filtering of advertisements. Some hackers have already experimented with ad blocking for reality through AR, and others have proposed it as a joke.
PublicAdCampaign and The Heavy Projects tested a new platform that uses Augmented Reality to virtually replace outdoor advertising with the artworks of some of the better known physical outdoor advertising takeover artists, including Ron English, PosterBoy, John Fekner, OX, and Dr. D.
Here is a video of the Artvertiser, an HUD AR app that replaces billboard ads and other everyday analog grime with artwork: