Ask HN: I need a recommendation for a sharing site for a small team?

Hi,

I've been asked to set up a site where a group of about 10 to 15 people can communicate and share files, in much the the same vein as Facebook and other social stream web apps.

I'd like to be able to host this on a small server somewhere like DigitalOcean, and if the amount of time spent setting up and maintaining it could be kept to a minimum that would be great.

Anybody got any recommendations?

Thanks

Edit: Sorry, forgot to mention that I would prefer free and open source projects that could be hosted anywhere.