a cross platform calendar tha'ts accessible?

hello. I did not know where to put this so here goes. I have a project that I'm working on and all of us receive invites to several things. The problem is this. The leader uses google calendar and it's a bit problematic on our mac and pcs. Is there a cross platform calendar like google calendar that can send out invites to these events, that is accessible for us to except said invites and stuff that the team leader can use? and they can create if they want to .ics files to put in our iPhones, for those of us with iPhones and iOS devices in general. Thanks all.