The Humble Game Making Bundle includes a vast variety of resources for all aspiring game developers. Although some of this content is optimized for use with versions of RPG Maker, all of the DRM free DLC packs are licensed for use with any engine, as indicated by the licenses that are packaged with their corresponding products.
At the bundle's launch, some of the DLC and asset packs were packaged with old licenses, which incorrectly stated that they could only be used with the RPG Maker. As of July 8, 2015, the correct license files — which permit these resources' use with any engine — are now included in the bundle.