We've recently launched iBegin Places - http://places.ibegin.com/ It is a
place for anyone to create, edit, and share informal space (neighborhood,
parks, pathways, etc). Built similar to how Wikipedia is set up, and it
lets you download the data via collection of points, JSON, Google Maps JS,
GeoRSS, or KML.

You can view a few samples:
Manhattan neighborhoods: http://places.ibegin.com/collections/view/2/
NYC subway (MTA): http://places.ibegin.com/collections/view/1/ (it isn't the
pathway that matters, but the location of the points).

There's a bit of voting, to move spaces from "unverified" to "verified." Spaces can be grouped into "collections" (Toronto and New York neighborhoods are good examples). The underlying rendering engine is Google Maps. This has some of the qualities of GeoCommons and OpenStreetMap. The big differences: in contrast to GeoCommons, you "create the data" on the site; in contrast to OpenStreetMap these are informal, not necessarily on the ground type of locations.

Most interesting to me is the idea that, like GeoCommons, it's simple to get the data out for use in your favorite app or platform.