The other mods and I have gotten together and written a first version of the topic page for this site. Please look it over. Feel free to suggest minor edits in comments. Major changes can be submitted as answers.
We have tried to take into account the wishes of the community as expressed in voted answers to topicality meta questions. However, please keep in mind that this is a living site and so some evolution as to what is or is not on-topic may occur over time.
One of the jobs that you, the community, must take up is voting to close questions that are off-topic. Mods can do this, and we will for questions that blatantly violate the topic guidelines. On the other hand, moderator votes-to-close are a Big Hammer, one that should be wielded sparingly so as to allow the community to grow and evolve. Also, please (politely) comment on the questions as to how or why you feel to question is off-topic.