During the last decade, the interest for e-learning systems has grown thanks to availability of bandwidth and powerful computers. Thus the e-learning has moved from specific environments to larger communities. The main challenge of the last generation e-learning systems is to provide courses tailored to different students backgrounds; this pushes the research to create an adaptive environment able to just-in-time craft the best path for each student. This paper deals with this problem, introducing a proposal of a system for e-learning which provides students with all formative paths moving from an initial to a desired knowledge, and where paths are adapted according to student needs and capabilities, and dynamically modified when such needs change. We also present a prototype of a web-based e-learning environment, through which students can follow dynamically adapted formative paths, also exploiting collaborative learning tools.