Design an Intranet for Employees of a Small Nonprofit

I am looking for a freelancer to design an employee intranet for a small nonprofit organization. The goal of the intranet is to facilitate communication and collaboration amongst the workforce. It should also provide efficient task tracking, including features like an integrated calendar and internal messaging system. The intranet should also have a medium level of custom branding content. For this project, I'm looking for an experienced freelancer who is well-versed in creating intranet systems that are optimized for a collaborative environment.
We have employees all over the world, and good security is a must. We are interested in the potential of creating an intranet with Google sites because it is free and we already use Google extensively.