Wiki has a feel of brainstorming, though it's not as interactive. You can do 10 minutes of brainstorming, and 30 minutes of analysis of the product of that brainstorming, and have something in 45 minutes. The pace on wiki is slower. You could write a page about an idea, or maybe a page about a bunch of ideas. Then you could come back in a week and see what's developed on that page.