FMG Inventory System, or FMGInvSys, is an Unreal Engine plugin, that features uniquely flexible item combinations and item widget setup.
Overview demo: https://vimeo.com/399060431
Custom logic demo: https://vimeo.com/399417379
Customized item widgets demo: https://vimeo.com/399406717
Either download or git-clone the repository. You'll get a directory named FMGInvSys-master. Then at the root directory of your project, create a new directory named Plugins, if it's not already there. Put FMGInvSys-master under the Plugins directory. The path to the plugin should be: X:/.../<ProjectName>/Plugins/FMGInvSys-master.
You may need to re-generate Visual Studio project files, for it to show up in your source code editor.
Then in your <ProjectName>.Build.cs, append "FMGInvSys" in this line of code:
PublicDependencyModuleNames.AddRange(new string[] { "Core", "CoreUObject", "Engine", "InputCore", "HeadMountedDisplay" });This adds the module to your project.
Currently the plugin supports UE 4.25.
The docs are in the Wiki.
For now, GitHub Issues seems to be a good place to ask your questions, in addition to submitting bug reports and suggestions.
More support may be offered when the project's first published, as there's likely going to be a lot of issues and needs for improvement. As the project gains more audience, and meanwhile grows to be more robust, the amount of support provided per user may gradually decline.