Rattan Simple Generator. That generator has 5 presets included and you can tweak then to generate some more variations. Dirt and aging options included. A good range of parameters are exposed.
For use on an unlimited number of commercial projects with no limits on sales or views.
For personal use and one commercial project (up to 2,000 sales or 20,000 views).
One copy to be used by a single user.
One installation by a single user.