Nextiva is an Arizona based business telephony and call center provider. It’s fairly well-known in US, but not much worldwide. Nextiva reviews are positive. If you are looking for a free Nextiva alternative that can be used as a call center or a unified communication platform, Bitrix24 is a great option. First, it’s free for 12 agents. Second, you get a choice between a cloud and an on-premise version (the latter one comes with open source code access). Third, Bitrix24 comes with a built-in CRM and sales automation tools. Finally, it offers a lot more unified collaboration tools than Nextiva (private social network, video conferencing, screen sharing, instant messaging, file sharing and so on).
* Please note that the information may have changed since the publication. For current prices and features please visit Bitrix24 pricing page.