I am looking for an open source collaborative web based application for to do lists (tasks and sub-tasks), shared documents, maybe a forum, google calendar, and google contacts. My sisters and I have taken over the care of our elderly mother, and we need a way to collaborate on what needs to be done, her doctor's appts, doctors' phone numbers, etc. I want the site to sit behind a user name/password and not be public on the net. 

Up to now, we have relied on email and spreadsheets. However, one uses Linux/OpenOffice/Android, one uses Windoze/MS Office, and on is on a Mac and iPad. The spreadsheet for tasks is not working very well.

My mother has a gmail account for her calendar and contacts, so I would like to just access those two apps in this mythical web application. 

I tried just giving my two sisters the password for my mom's gmail account, but that was a challenge for one of them (and neither use gmail nor are they willing to get a gmail account). So I need something simple.

I looked at GQueues, but one needs a gmail account to access a shared version of the app. Plus, the app has an annual fee for all the features (calendar and contact integration).

I looked at Plone, but can't seem to find a simple to do list for it. 

I looked at django and some of the cms offerings, but that approach seems to require a fair amount of customization, and I need to be up and running now.

I tried google sites as a front end to her gmail account, but one has to have a gmail account to access the site, even if it is shared with another account (I tried it with my yahoo account).

I am currently using google to look at other apps, so if you have any suggestions, please let me know!

Thanks,

Mark