3CX, Yate - Yet Another Telephony Engine, CloudTalk.io, sipXcom, FreeSWITCH, Elastix, FusionPBX, opensips, Wazo, Kamailio, Starfish PBX, VoipSwitch, MiRTA PBX, RingCentral Engage Digital, Avaya Voice Portal, Vodia Networks, Thirdlane Business Phone System, PBXware, Genesys are some alternatives to FreePBX.