Asterisk - An open source telephony switching and private branch exchange service for Linux.

InsightSquared - #1 for Salesforce.com Pipeline forecasting, profitability analysis, activity tracking: all the small business intelligence you need. Works using CRM data and automatic syncing.

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.

Aviso - Aviso provides predictive analytics software to help sales organizations optimize their performance and exceed revenue goals using machine learning algorithms and portfolio management techniques.

Kamailio - Kamailio® (successor of former OpenSER and SER) is an open source SIP server released under...

Sidekick by Hubspot - Customer insight integrated with your email tools.