We're making a web app, PHP with CodeIgniter, that among other things, sets up meetings between two people. User A sets up a meeting with User B, then User B can accept or reject it. User B gets an email detailing the meeting, giving them links back to the site to accept or reject. Then they can both log into the app and view their calendars.

I'm now being asked to allow these events to be added to user's personal calendars, such as you find on your iphone, or outlook or thunderbird or lotus notes ... etc.

I can work out producing an ICS file for new events that could be added to the user's calendars, but is it possible for changes made in the user's calendar to be sent back to the server to keep the app and the users' calendars in sync?

I'm thinking no... but you guys know lots of stuff

You can do that directly in Outlook.

I've looked into this a while back and the only solution I could come up with was a stub app on the client computer that monitored the calendar and fired back to the server when a change was made or a new event was added.

It's how Google's calendar sync works - you need something on the client machine.

Unless things have changed in the last 12 months of course...

P~

I would recommend looking at a CalDAV implementation. http://www.davical.org/