I'd like to point out Anki, an open source (GPL 3) virtual flashcard program I've been using. Anki runs on all major PC platforms (and an impressive array of mobile devices), and is feature-rich. It has a plug-in architecture. Cards can contain not just text but also images and audio files. Anki supports LaTeX, so it should be easy to put mathematical formulas on cards. Use of card decks is very flexible (including an easy way to have cards representing difficult concepts repeat sooner than cards representing easy concepts). It is easy to create or import card decks, and you can share card decks (and plug-ins) with other people through their AnkiWeb site. (Disclaimer: I have not looked at the available shared decks, nor have I looked at any plug-ins. The basic download fills my needs.)
My use for Anki has been to learn my students names. At the outset of each semester, I acquire a class list with student photos, strip out the photos, and turn them into an Anki deck. During idle moments at coffee shops, I play the decks and learn to associate names with faces. (Addressing students by name on the first day of class freaks them out; I think they tend to be more docile thereafter.)
I'm not a big fan of rote memorization in education, but I suppose it has its place. I could see using Anki to learn formulas from queuing theory (for instance, "M/M/1 steady-state queue length" on the front, the corresponding formula on the back) or perhaps some terminology from linear programming (graph of a feasible region and an objective hyperplane tangent along an edge on the front, "multiple optima" on the back). As there are more things in heaven and earth than are dreamt of in my philosophy, I suppose there are more ways Anki could be used in the teaching of operations research.