3CX Phone System for Windows is an award-winning software-based VoIP PBX that replaces traditional proprietary hardware PBX. It is based on the SIP standard and supports most popular SIP phones, VoIP Gateways, VoIP service providers and PSTN phone lines. It is easy to manage by system administrators as it integrates well with Windows Network infrastructure.
You can view the brochure(PDF) here or download 3CX Phone System for Windows here. You can read more about 3CX and VoIP on the 3CX VoIP Blog.