Nominatim is under github: https://github.com/openstreetmap/Nominatim

Please note many mobile OSM-based apps do not use Nominatim, they all developed their own search mechanism.

And as others said, for on-line searches there is always Overpass. This means that all tools exist for those “non-commercial” searches, but http://osm.org is not meant to compete with Google. Therefore they are not integrated into 1 package.