While there is meanwhile a plethora of Learning Content Management Systems, the collaborative, community- based creation of rich e-learning content is still not sufficiently well supported. There have been some efforts to apply the Ward Cunningham's wiki paradigm to the creation of e-learning content. However, the paradigm was mainly only applied to unstructured, textual content and can not be used in SCORM-compliant systems. To address the issue we develop the CrowdLearn concept to exploit the wisdom, creativity and productivity of the crowd for the creation of rich, deep-semantically structured e-learning content. The CrowdLearn con- cept combines the wiki style for collaborative content authoring with SCORM requirements for re-usability. Therefore, it enables splitting the learning material into Learning Objects LOs with an adjustable level of granularity. In order to realize the CrowdLearn concept, a novel data model called WikiApp is devised. The WikiApp data model is a refinement of the traditional entity-relationship data model with further emphasis on collaborative social activities and structured content authoring. We implement and evaluate the CrowdLearn approach with SlideWiki---an educational platform dealing with presentations and questionnaires. The article also comprises results of a usability evaluation with real students.