FusionPBX is a multi-tenant phone system that can support many customers on a single platform. It is based on FreeSWITCH and is easy to set up, configure, and manage. With addon soft clients, it makes it easy for employees to work remote!
Download FusionPBX here: https://www.fusionpbx.com/download
View the Voxtelesys guides here: https://voxtelesys.com/tutorials/fusion-pbx