Well, Postworkshop isn't designed to replace things like the Gimp or Photoshop. It's more a quick and easy way to apply overarching effects to your whole layer. As far as I know it doesn't have brushes, pens etc.

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Hardware: AMD Ryzen 9 3900X/MSI MAG570 Tomahawk X570/Zotac Geforce GTX 1650 Super 4GB/32GB OLOy RAM

Software: Windows 10 Professional/Poser Pro 11/Photoshop/Postworkshop 3