MailChimp - MailChimp is the best way to design, send, and share email newsletters.
freepbx - FreePBX is a web-based open source GUI that controls and manages Asterisk (PBX).
Brevo - Innovative online Email Marketing solution to manage your contacts, create & send your newsletters and track your results. More than 80 000 clients. Best prices and attractive features.
Asterisk - An open source telephony switching and private branch exchange service for Linux.
Campaign Monitor - Email marketing software built for designers and their clients to run successful email campaigns.
FreeSWITCH - FreeSWITCH is an open-source media application designed to support popular protools such as SIP and WebRTC and provides a platform to develop voice and video applications.