Telegram
Description: Telegram is a cloud-based instant messaging and voice over IP service. It offers end-to-end encrypted video calling, file sharing, and several other features. Telegram clients exist for both mobile and desktop systems.
Type: software
Pricing: Free
Yate - Yet Another Telephony Engine
Description: Yate is an open-source telephony engine and server for VoIP and legacy telephone infrastructure. It supports multiple protocols and interfaces for building communications solutions.
Type: software
Pricing: Open Source