Texture Painting on regular objects

Is there some way to paint textures on regular game objects? An extension or anything? I was experimenting with the terrain painter and it is really nice, but the terrain won’t work with my current level design.

Now that would be one hell of a plugin (in a positive sense). It is possible to write a script that is able to do that, but no one has done this so far, as it would be very involved.
Terrains are seamless in their UV-layout so it’s almost a no-brainer to paint that, with Meshes you are not guaranteed to have that property. This really makes it much more complicated.

I don’t know of any such functionality in Unity but many modelling tools have it (like Blender, which is free).