Tordanik
(Tobias Knerr)
2
There are several 3rd party APIs that serve OSM data, including the Overpass_API and different providers of an XAPI interface (e.g. Mapquest).
The APIs mentioned above have (albeit limited) filter capabilities. For more flexibility, you use tools such as Osmosis or Osmfilter. Osmosis can also be used to merge files. Calling them from a server script depending on users’ inputs should absolutely be possible.