If you are already familiar with FreeSWITCH then you will probably understand how these two are connected. FusionPBX is an open source project providing highly adjustable interface to the multi-platform voice switch called FreeSWITCH which has high level of scalability and robustness. FusionPBX is flexible enough to be compatible with different operating systems and your preferable hardware. FusionPBX provides GUI for a batch of features such as unlimited extensions, voicemail-to-email, call parking, time conditions, follow me, music on hold, queues, high density T1/E1 circuits, etc. License of FusionPBX is the MPL 1.1 (Mozilla Public License).