I created a tool to calculate an elevation at the point of a click on the OSM map: http://ausleuchtung.ch/elevation/
The elevation is calculated as an average from the values of the ele=* keys found around the click in the radius of 1 (or 2, or 3) kilometers.
I decided to write this simple application after I read an excellent article GPS Altitude vs Pressure Altitude.
For some areas of the world there is a lot of elevation data in the OSM database, and for some there is practically none. I think it is due to the misunderstanding about the difference between GPS Altitude and Pressure Altitude. The article makes it clear that both approaches are not perfect, but these are all what we've got, and we are to use one or another.
The application seems to be simple because all the heavy lifting is done by the Overpass API, OSM, and the Leaflet.
Elevation data could be useful for many purposes. For example, for planning a hiking or a cycling route, for planning a RPAS flight, for water management, etc. For example, if a hiking route starts at the altitude of 400 meters, and ends at 1600 meters, then it is immediately clear that it would be a hard day.
I also plan from now on to measure and add more ele=* data to the OSM.
Feedback and suggestions are very welcome.