Simple Image Edge Preserving Filter
Recently I have seen the paper Hui Yin, Yuanhao Gong, Guoping Qiu - Side Window Filtering.
They suggest a really simple filtering framework for Edge Preserving Filter:

Basically, what they suggest is filtering the image with a set of filter based on the Box Filter.
This filter set is basically composed of 8 filters with different orientations and sub sets of the Box Filter (As seen in the figure above).
Once you apply all filters (Which each of them can be implemented very efficiently by all the efficient implementations available for Box Filtering) you chose, on a per pixel basis, the one most similar to the original pixel.
Applying it by iterations, yields very efficient and very good filter.
I took the Lena Image:

I applied 40 iterations of the filter (Link to 75 Iterations):

The full code is available on my StackExchange Signal Processing Q74674 GitHub Repository.