The Darwin Calendar Server is a standards-compliant server that allows multiple users to collaboratively share calendaring information. It provides a shared location on the network to store schedules, and allows users to send each other and manage invitations.
This guide outlines how to enable the built-in VPN service (vpnd) in client versions of OS X, as Apple has neglected to mention (let alone explain) the possibility under non-server editions of OS X. Standard disclaimer applies, as always: You are 100% responsible for your own actions. Using this guide, visiting a link, downloading a program, in short, living, is done entirely at your own risk (and joy).