This is a little program which lets you easily generate OSM contour lines from NASA SRTM data. It was initially created as replacement for srtm2osm which stopped working when the NASA changed the server and started distributing the raw SRTM data via http instead of ftp. In the meanwhile, srtm2osm is working again due to the efforts of bomm.
However, phyghtmap has some advantages compared to srtm2osm. One is that you won't need a C# runtime environment installed on your machine. Another important thing is that phyghtmap generates already tiled data. Furthermore, phyghtmap seems to slightly outperform srtm2osm. If you are using a multi-core machine and are running a POSIX compliant operating system you can use a very simple form of parallelization and the advance will be dramatical.
Note that the intended use is not to upload generated contour OSM data to the OSM servers but to use it for fancy maps.
For a detailed help, run
phyghtmap --help
on the console.