I have been having this doubt for quite a while. An inverter basically is a power electronic equipment that converts DC voltage in AC voltage for powering loads that work on AC supply.So this means that the inverter switches operate at a frequency of 50Hz (for India).
Astable multivibrators also does the same job of converted a DC voltage into a alternating square wave voltage. Also I've found that research is going on in elimination of harmonics from inverters in order to obtain pure sine wave. Instead of that, why not use a simple RC phase shift oscillator or wien bridge oscillator designed to oscillate at 50 Hertz? Is it difficult to design? What are the complications faced in doing so?