The Mr. Clean Magic Eraser is a great tool for cleaning when your traditional cleaning products don't seem to work. It seems to work as an extremley mild abrasive to remove dirt from surfaces.
To use it, you simple wet the sponge-like eraser under running tap water, ring it out, and begin gently wiping the surface you intend to clean. Most recently I've used it on the walls of my home after my toddler enjoyed the pleasure of dragging crayons all over them. I tried with paper towels and household all purpose cleaner to begin with and made very little progress. I luckily had a magic eraser deep under my sink and managed to find it. It worked amazingly well on my crayon situation. There is not a trace of purple, black, orange or any color crayon for that matter, remaining on my walls.
This item also works very well on my counter tops for removing coffee stains, tea stains and red wine stains.
The one drawback is that after a short while the eraser begins to crumble and flatten out, rendering it somewhat useless. For that reason would not recommend these for daily use but for special cleaning events that require extra help.