Flock provides channels where multiple users on the channel can brainstorm/chat on any particular idea or project.
It comes with a set of inbuilt productivity tools, one of them is the polling app - that'll help you consider everyone's opinion when taking a decision.
It's also a cross-platform app, available across Mac, Windows, Android, Iphone and Chrome.
There's ton of features for collaboration. Also, did I mention it's free?