AHA! is a simple Web-based adaptive hypermedia system. Because of this simplicity it has been studied and experimented with in several research groups. This paper identifies shortcomings in AHA! and presents AHA! version 2.0 which tries to overcome the known problems with AHA! while maintaining its biggest asset: simplicity. The paper illustrates how different user modeling and adaptation aspects can be expressed in the new AHA! system, features that would be difficult in the old system, and impossible in most other systems. Discussion highlights include: introduction and background on the development of the AHA! system; the domain model/ adaptation model in AHA! version 2.0; user model in AHA! version 2.0; document (page) formats; examples of AHA! applications; and future work. (Contains 13 references.) (Author/AEF)