Here are details of the release from Quixel:
Yes, we are now making dDo as we know it free. Not only that but we have also spent some love and care on improving features, stability and UI. This version will have limited support but will still be updated as per your needs.
We sincerely hope that you who own dDo will not feel let down that you paid for something that will now be free, but rest assured we will do our best to make it up to you with a free upgrade to the all new, arguably more bad-ass, DDO.
So what exactly is dDO? Here is the official description:
DDO empowers artists with tools to make better textures. DynaMask unlocks extreme masking control over ultra-real wear & tear and shape based coloration. The 100% customizable Smart Materials empowers artists with the easiest PBR workflow to date. And Fusion lets you plug DDO right into any app.
Perhaps of more use is actually seeing dDo in action.
Just a bit of a heads-up… dDo works in Photoshop, and thus requires Photoshop. Without Photoshop dDo is of no use to you.