ProgZoo is intended to be a resource for learner programmers and a reference for practitioners or programming.
The tutorial material is aimed at first year Undergraduates with no previous programming experience. It attempts to be "wide spectrum" in that it includes many easy questions for the majority of students and a few harder questions for more able students. The tutorials are for people don't know what they don't know.
The reference material is supposed to show the simple, obvious cases first. It should be particularly useful for programmers who know how to do something in one language but need to know how to do it in another. The reference material is for people who know what they don't know.
There is a great deal of missing material. Mostly, the Java pages have most tutorial material - from these pages you can access other languages, please help out by copying a Java tutorial then translate it into the programming language of choice. Completing the missing tutorial material is a task for people who don't know what they know.
Lucky people who known what they know could help most by improving the structure of the site and the organization of the tutorials and guides.