I'm making Q/A for high school students.Most of them know well and can contribute more than in one topic, so I want to make them able to select topics in which they want to participate. This would be done in ajax, when subject name is clicked, All activity, Questions, Hot, Unanswered, Tags would be updated to include all selected sites.
Example of what I'm talking about looks like that.
I want to know how to achieve this ?
P.S. I can see I may be able to easier achieve this by tweaking built-in categories, but I plan expanding to even more diverse Q&A sites later and want to be able to have stand-alone site with one topic, as well as one page to filter from which site's databases to load questions, tags, users and other info.