Train Master features daily quizzes, each day of the week focused on a different category, including routes, trains, train cars, and history. On Friday, you get to choose the topic, and on Saturday, you are tested from within all the topics. This is actually starting to sound like work.
The developers seem to recognize the work-like aspect, as well. On some Sundays you get to take a day off from quizzing-- to go on a virtual date with one of the mascot characters at an interesting railroad- or train-related location.