Officially, a Sprush is a cross between a spatula and a tint brush. I have been using sprushes for years to perform relaxer touch-ups. They can be used for haircolor application as well, but I prefer a regular tint brush for color services.
Recently, I added the new "Optimum" sprush to my collection. It is the center sprush in the picture. Do you notice that the surface of this special sprush is textured with ridges? The rest of the sprushes in the picture all have smooth spatula surfaces. I like the new textured sprush because I can pick up heavier amounts of relaxer and apply to new growth without the whole glob falling into one place. The textured sprush seems to hold the relaxer in place on the sprush until I am ready for it. This feature saves a few application strokes.
The company that makes this tool is called Sprush.