Answering student questions as they work outside class If your students are like mine, they do a lot of their work outside my view; at home, on weekends, etc. But as they work they sometimes get stuck. They get questions for which they need the answers in order to continue. Sometimes it is a long time before the next class period or office hour. 

Suppose that you would like to be able to answer their questions as they arise, but without disadvantaging other students who may have the same question but didn't think to ask. Sometimes, in fact, a student finds an inconsistency in something you said or gave them, and needs a correction before they can continue. 

What tools and mechanisms do you find useful for letting students get necessary answers, at times you are not in class or office hours? I'm looking for actual solutions, not guesses about what might work or which make someone's life (mine) miserable. I'm pretty sure that giving out my cell phone number fails on too many levels to consider.
Threaded discussion forums allow everyone to see all questions and answers and to post questions and receive answers at any time that you find convenient to check in and update. I have used this in online teaching before. It works very well.

Actually, I don't know of anything else that does or would work. I would love to hear about other possibilities.