Dovetail mounts and holders for the MakerGrid clip system. You can mount MakerGrid parts onto shelves, walls or anything else you can screw an M4 (or comparable) screw into.
The advantage is the flexibility with which you can mount MakerGrid things anywhere. I use it currently to extend my self designed spool holder (see my other files on Github or Thingiverse for instance).
The most current designs for the MakerGrid you will find no my GitHub account: https://github.com/WeirdConstructor/3DPrining_MakerGrid
The also the MakerGrid Base Parts: https://www.prusaprinters.org/prints/123580-makergrid-base-parts
The author hasn't provided the model origin yet.