Adobe Substance 3D Painter is described as 'Advanced software for 3D asset texturing with smart materials and real-time rendering for lifelike results, suitable for both photorealism and stylized art' and is a 3D Painting app in the photos & graphics category. There are more than 10 alternatives to Adobe Substance 3D Painter for a variety of platforms, including Windows, Mac, Linux, Web-based and Self-Hosted apps. The best Adobe Substance 3D Painter alternative is ArmorPaint. It's not free, so if you're looking for a free alternative, you could try InstaMAT or Quixel Mixer. Other great apps like Adobe Substance 3D Painter are 3D-Coat, Autodesk Mudbox, Quixel Suite and MARI.
PixaFlux is more similar to Substance Designer rather than Substance Painter.