Does anyone know a simple, photo editing software?

I'm looking for a SIMPLE photo editing software where, (besides the standard brightness, etc features,) that will specifically crop with rule of thirds lines, straighten picture, and resize without losing DPI. For years I used Microsoft's Picture IT an would like to find a similar program. I don't need all the bells and whistles. I currently own Corral Painter on my PC and hardly ever use it. But I would like to use my MAC exclusively. Thank you.