Decal On The Shell is a Blender addon from Yey! for adding decals to 3D models. It's positioned as an addition to the Black Mesh addon to improve the quality of models, it runs on Blender 3.2 and later, and it is described as easy to use.
The addon includes 50+ decals and works without textures or normal maps. Decals apply to meshes that use the SubD modifier. You can store your own sets of decals as blend files inside the addonPath/DecalOnTheShell/Decals_Sets folder, and the addon includes tools to prepare decals through vertex weights and modifiers.
Documentation is available, along with a Discord server and a BlenderArtists thread. A demo video is also available, and the addon holds a five-star rating from four reviews. Distributed under the GPL license, it's listed here as free.