Just adds a wrench. This is used to rotate all different kinds of blocks, such as stairs, slabs, logs, doors, trapdoors, repeaters, comparators, etc. If there is a block that seems like it could be rotated, but the wrench doesn't work on it, just add it to the "justawrench:wrenchables" tag in a datapack to try it!
For devs, there is an API for compatibility, see the wiki.

