A simple Minecraft-mod that makes all slabs placeable vertically as well as horizontally. Note that this mod does not add new items or blocks, it just modifies the existing slab blocks.
While this mod aims to work with other mods that add slabs, it is not guaranteed that all features, especially the block models, work as expected.
In case your game has missing textures, you can do something about it yourself. More about this in Fixing broken slab textures