Free Online Project Management

[tinoman]

Hello People,

I am looking for an online teamwork solution, where both systems mac and pc can contribute thoughts, notes and little images for brainstorming purposes.

Like OmniGraffle, but Online and therefore accessible from both platforms through any HTML browser.

I was looking up CMS but there are so many and they want to be so sophisticated but no need. I am looking for simple, non-linear solutions. Maybe a blogger? Better a Wiki. But what is simple and even free? And can you upload pictures?

Thank you for any directions