No songs on 9/11? I can think of a couple, including Tom Paxton's The Bravest, dedicated to the fire and rescue service of New York. And I have sung it on several of the anniversaries of the event, although it's a tough one.
I don't think anyone has yet mentioned songwriting competitions, which occur at several folk festivals and clubs I go to here. The rules vary from place to place, but phrases such as "to be written in traditional style" or "in the folk idiom" crop up. But the entries are often pretty eclectic, with subject matter equally wide-ranging. A very few of these songs take on a life of their own: thinking of Karine Polwart's "Whaur dae ye lie" or Steven Clark's "Coming Home", for example.