Shaders are some code (probably the most common version now is GLSL, OpenGL Shading Language) written to calculate the colour of pixels and vertices. They run on the GPU, they can do some awesome stuff; triple A games are probably the most common place you’d find these being used, probably also in animation. Sharing them would presumably just mean a site where you can write shaders and browse other people’s shaders.
It would be like Replit(or any other online IDE), but specifically designed to make shaders, and only shaders. Those shaders can be shared with other people publicly. I may add a conversion feature for converting a shader ( GLSL Format ) to different shader formats.