Multiply have posted that they’ll no longer exist as a networking site from December 1, so that means that we’ll no longer be able to use it to organise events.
I am unable to use Facebook (it’s blocked from work), so that isn’t an option.
Does anyone have any suggestions for a new site that allows calendars, etc? Has anyone tried Google Plus?

Google plus is the only one that I;ve found that isn’t blocked by my work. The google calendar is easy to use and integrates well with my phone. My only complaint is that many of my friends are not on G+ regularly.
My group has been using doodle for years. http://Www.doodle.com. It’s intended as a polling site, but we poll availability for dates, instead. Might be worth checking.