This royalty-free set was made exclusively for the smudge tool on Adobe Photoshop CS5 – which means it probably won't load on previous versions of the software. I didn’t test it with other tools, but feel free if you want to change the settings and use it as a paintbrush or eraser, etc. And... yeah, if you do use it, I would love to receive credit and/or see the artworks done with these brushes.
Of course I was forgetting to add something in this description! That great cardboard texture, used on the preview, was provided by ~Galloping-Textures. You can download it here. And don't forget to check the rest of the gallery for more amazing resources.