AwesomeBump is a free and open source program written using Qt library designed to generate normal, height, specular or ambient occlusion, metallic, roughness textures from a single image. Additional features like material textures or grunge maps are available. Since the image processing is done in 99% on GPU the program runs very fast and all the parameters can be changed in real time. AB was made to be a new alternative to known gimp plugin called Insane Bump or commercial tool: Crazy Bump.
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Pro Feature complete
Supports great features, such as the addition of grunge maps, supports tessellation, and has a beautiful 3d view port.
Pro Free and open-source
Being open source, along with the price of nothing makes this software very compelling to use.
Pro Cross platform
This software is cross platform, so you can integrate it into your work flow without worrying to much about your operating system (Linux, Mac, and Windows).
The first few times using the software, you may have a hard time getting what you want. That is mostly due to the slew of features, and slightly confusing interface.
Con Requires open GL 3.30 or higher
Although the pbr view port looks great, it does come with the drawback that you will have to have support for open GL 3.30 or higher, and set it up before hand (if its not already set up on your computer).