In order to map some objects, since pre-2.5 versions, blender users had the support of many tools, one of them was the Object map input:
with this technique, you could map a texture to an object referencing the mapping to another object, like an empty, a cube or a more complex 3d object.
Nowadays things changed a lot and with the advent of cycles, in Blender 2.61, artists from all over the world, tried this new render engine that supports only its node materials setting, meaning that the old fascinated easy way to map a texture from an object was old and dead…
In some cases the uv map cannot be used with some particular situation, like the triangulation or ngons faces; in other situations the mesh is just too complex to be correctly unwrapped.
In those cases there is the pretty new modifier that provide a new way to map texture referenced to position,scale and rotation of another object: The UV Project modifier
Its quite simple to use:
These method worlds for cycles but also for the internal renderer, so you could map strange and non usual UV configuration as well
With a parented object, you can control the whole project modifier projectors through a single object: