The Six Disciplines RightPage app is the easiest and most comprehensive brainstorming tool I've used are either too simple, too complex, standalone, or don't offer the kind of flexibility that you'd expect. RightPage sure beats using flip charts or Post-It notes!) On top of that, the RightPage app is free, it's mobile (any web-based device works - laptops, tablets, smartphones), it supports remote brainstorming, as well as voting (and re-voting) on brainstorming items. Review collected by and hosted on G2.com.
There's really not much to dislike about Six Disciplines RightPage app - it's free, it's easy to register, it has an simple design, making it easy to use, it has an online video to show you how to use it, it's very flexible, yet it's still powerful enough to handle tough brainstorming exercises. Review collected by and hosted on G2.com.