GroupMap is intuitive. It appears you don't need any special skills to use it or to facilitate even the largest group. They seem to have every template I could ever want and the ability to customize the design and functionality of each. It has all the biggies like brainstorming, SWOT analysis, SOAR Analysis, Business Model Canvas, Urgent Important MAtrix etc. plus many industry-specific templates like Agile retrospective and KWHLAQ. Groups can attach files, make comments, vote on priorities and more. The anonymity function is excellent to prevent groupthink.