For example, the economy kind of just happened. People needed to eat, to trade, etc. While explicit actions have been taken at each step, no one said let's build a "stock market" 2000 years ago. Well, I doubt it.
Another abstract example might be the creation of towns along trade routes. Some towns started by just a trading post or an inn situated on a crossroads. Soon enough, a few stores, a couple houses, a few farms and you have a town. No one said "let's build a town here" but it just kinda happened.
A more concrete example might be the creation of trails through a forest. Trails generally form when one person travels along one path, blazing it as he goes. Then another person sees the underbrush squashed a bit and decides to follow the first person. Repeat. Over time, the ground becomes compacted and the underbrush does not grow back (or if it does, it gets trampled again). No one drew a line on the map and said, "We're going to build a trail here." (of course, sometimes this does happen, but we're not talking about professionally managed trails). It was exactly this metaphor of trails, that inspired TrailFire to develop and offer its free social collaboration tool and annotation service.
A stronger version of this phenomenon is common in nature, called stigmergy. Social insects almost universally collaborate "incidentally", except their behaviour is hardwired as instinct. In many cases, such as an ant laying a trail to a food source, pheromones are deposited into the environment so that if another ant accidentally wanders over the trail it will be compelled to follow it (with some probability). In another example, ants will collect dead bodies into round piles by following the simple rules: 1. If you see a carcass and you aren't carrying anything, pick it up; 2. If you are carrying a carcass and you see another; drop the carcass.
In both these cases, it isn't the ants conducting the show, but the environment--the structure that eventually emerges--that controls the system. In some ways, things like WikiBadge?s and editor notes are analogous to pheromones, sometimes influencing friendly editors years after the original author has left. BackLinks are also analogous to the pile-building behaviour (see IncidentalCollaboration#BackLinkAnecdote).
The basic theme behind all of these is that small local events (aka "incidents") build into more complex global emergent behaviour. IncidentalCollaborations are interesting because they kind of "evolve" into the most natural solution. I would even hazard a guess that all incidental collaborations form out of necessity; as problems become very hard, people are forced to work together to solve them.
That is until people start noticing them. Then they analyze them and feed back their analysis skewing the system so it requires further analysis. The economy is an example of this. The stock market has very little grounded meaning nowadays.
I find it interesting that I incidentally collaborated with myself. While I wrote the original text, I had completely forgotten about it. I wanted to write about stigmergy as I'm learning about ALife:SwarmIntelligence, and the analogy between pheromones and WikiBadge?s came to mind. WikiBadge? didn't exist, so I search for BackLinks to WikiBadge? and found this page. BackLinking is an example of the wiki controlling us as it is ArchitecturalCollaboration?. -- SunirShah