This literally stops you from punching trees. It does so very unoriginally, allowing you to make a flint hatchet like so:

Flint Hatchet Crafting Recipe

and making string with plant fiber, gotten when breaking like any plant you can think of (except flowers), like so:

Plant Fiber Crafting String

Where things get interesting is when you try to mine stone like usual and it doesnt drop you anything, where you have to resort to breaking down Light Stone to get Loose Stones.

Light Stone

Light Stone can be found in tall boulders in flat biomes, or in blobs under the world, the lowest at y56. Using the Loose Stones, you can make cobblestone like so:

Cobblestone Crafting Recipe

This mod was made for a modpack im working on for a youtube video, and was added to make the game just slightly harder.

If you want to add compatibility, with tags, here are my custom ones:

survival_of_the_fittest:fiber_harvestable - Blocks that can produce Plant Fiber upon breaking.

c:flatland - Biomes the light stone boulder spawn in, by design flat biomes only.

Survival O' the Fittest