It's been a lot of time since I started on this.
There are core, material, effect systems.
The material system allows creating whatever material you want. There're properties & you can use GLSL snippets. (supported transparency, simple layering, normal mapping, and every property is runtime changeable)
The effect system allows the creation of various effects controlled by modules.
The pipeline uses deferred shading, there're also cascade shadow maps, point lights, PCF, SSAO.
The 'core' is an OpenGL module that auto binds textures, auto binds different types of buffers, supports their streaming, texture compression, caches state, supports some extensions like bindless textures, direct state access.
