WOOM is planned to use Cairo, a PDF imaging model that has similar nature to the libart except that it aims to have hardware acceleration in future (This including their OpenGL plan). WOOM will use Cairo to render on each window. But will has its own implementation of windowing system which first will base on Cairo and will switch the infrastructure to OpenGL whenever it is possible.
This is the most recent class diagram. WOOM is designed as a server-client model. The client is working in a sense of a GNUstep backend. Using DO or network socket for the communication.
get the diagram (require OmniGraffle/not free, don't buy it)
(c) Copyright 2002 CSFSUH, anonymous coder