Mail with Calender

[Noturns]

I'm looking for a webserver with calender support for our Plesk server.

Features
- View shared calenders
- Calender Invitations

I have looked at plugins for roundcube however found the community and deployment to complicated.
I looked at Horde this worked out of the box but the layout is a bit outdated.

I'm looking at Google Apps for Work, but i would need to pay for every user.

Are there any alternatives?

Best regards,