A new paper of mine, Learning sequences, is now available on the arXiv. It's intended as a chapter in Knowledge Spaces: Applications in Education (Falmagne, Doble, and Hu, eds., to appear sometime after the rest of the chapters are written) and describes an application in which a computer tests a human student to find a combinatorial description of what the student already knows and what the student is ready to learn.

If I were aiming it at a different audience, I might equally well have titled it "How to implement an antimatroid". The main point of the paper, stripped of its computerized education application, is to advocate using a small set of basic words of an antimatroid as a data structure to represent the antimatroid, and to describe how various basic operations such as listing all sets in the antimatroid may be performed efficiently using this data structure.

ETA: [info]atheorist points out another potential application in tracking game character skills.