4PSA VoipNow Express is a Linux IP PBX software with 10 phone extensions, designed for hosted VoIP PBX services or in-house IP softswitch. It's free and can be easily upgraded to the full-featured multi-tenant Professional edition.

The Express Free edition of 4PSA VoipNow offers basic PBX features, supporting up to ten phone extensions. On the other hand, the Professional edition increases scalability and provides advanced PBX features like IVRs, group management, calling cards, callback, remote conferences and call queues.
The software is packed with standard PBX features like SIP and IAX channels support, caller ID, call management, call recording, voicemail, DND (do not disturb) function, call cascading, ring groups, music on hold, DID management, and call monitoring.
Moreover, the advanced PBX features include intelligent cost call routing and PTSN fallback, Incoming call rules, local or public conferencing, fax and voicemail to Inbox, Auto attendant (IVR) with text2speech, call center integration with call queues, sophisticated distribution algorithms and advanced graph reports and statistics, callback service, calling card, and call screening.
4PSA VoipNow further offers robust user management, allowing users to employ multi-tenant software architecture, four levels of control for hosted services (admin, reseller, client, extension), web-based interface, group management, individual permissions, and limits for each account, single sign-on, and SOAP API for integration with third-party apps.
The software comes equipped with a real-time billing engine, time intervals management, prepaid and postpaid billing plans, calling card billing, callback billing, and call center-grade queues report. The system can sustain several hundred extensions even on an entry-level server.
The ZIP file contains a Linux shell installer, and the software can also be downloaded in the ISO, VMware Image or Virtuozzo/OpenVZ format. For more information about the software installation, check out the official website. Overall, 4PSA VoipNow is an all-in-one software suite for all your PBX needs.
Version 1.6.2: CallNow Center, Restore, no kernel modules, Parallels Plesk integration