Waves on a string, ripples on a pond are transverse waves generated by mechanical energy and in the simplest form oscillations. Sound also is a form of energy and basically oscillations. What makes sound unique in the fact that it is longitudinal ?
In order for mechanical waves to propagate there needs to be some form of "restoring force" that tries to bring the system back to equilibrium. For longitudinal waves in gases this restoring force is supplied by pressure in the medium. However, there is no restoring force in a gas for bulk shear movement of the gas particles. Therefore, there is no transverse wave propagation in gases.
However, as mentioned in the comments, sound can also propagate transversely through solids, where there is a restoring force due to shear movement. The fact that both bulk transverse and longitudinal waves can propagate through solids, but only bulk longitudinal waves can propagate through fluids, is important in studying seismic waves, since the Earth is made up of both solid and fluid components.