Grit and Grime is a pack of two free brushes for the Procreate iOS app. The set comes with a dark and light version. Both are pressure sensitive and feature gritty textures, fantastic for adding some extra style to your lettering. I use these brushes a lot when I make paint streak lettering because it gives the base letters a textured look before you even start adding the streaks in. Download them directly here (dark, light) or from Dropbox here (dark, light).
Here are some examples of what you can make using these brushes and the paint streak technique: