HowTo make a map like the one on the user site of OSM? (nearby users)

Hi,

I’ve not found any hints on this: How can one create a map like the one on the user site, where the nearby users are displayed? Or more generally: How can I embed a OSM map on which different users can set their positions and then you’ll see all users?

An example with google maps you can find here (for those who haven’t understand what I want ;)) → http://ubuntuusers.de/map/ (you’ve to zoom in → germany)