SwarmSketch is "collective sketching of the collective consciousness", to quote the site. A current topic is chosen and then each visitor given the opportunity to draw one line on an emerging canvas.
Once drawn, the line is saved, and you are given the opportunity to vote on the opacity of other lines.
As well as the face-value collaborative/open-community drive of this project, from spatial point of view it is interesting that your contribution is affected as currency; limited by a determined quantity of your contribution (in this case, the length of your line in pixels).
It is worth questioning why in an open-source sketch, a limitation is imposed that effectively acts as the currency of information.