Slack is an online service for correspondence. Suitable for small team and big company. The system is a replacement for Skype for the interviews. Slack is integration active conversations with other applications. It allows full monitoring of the progress of work on various projects with a single interface and eliminate unnecessary information.
Tawk.to is online chat gives you the opportunity to provide support to users in real time. Tawk.to gives you the opportunity to observe the behavior of the visitors and to communicate with them, when they need it.
onpbx - it's a phone platform. On the basis of the platform of telephone services to increase sales. The main service virtual PBX, which is complemented by the integration and can be expanded with API.