Google voice and video chat
Call anywhere in the US and Canada for free and get low rates for other countries with this small plug-in, right from within Gmail.
Share photos, videos, music, files, documents and more between all of your devices. File sharing from phone to PC, phone to phone, PC to phone, PC to tablet.
WhatsApp for PC is a cross-platform mobile messaging app which allows you to exchange messages without having to pay for SMS.
Zoom is an easy, reliable cloud platform for video and audio conferencing, chat, and webinars across mobile, desktop, and room systems.
WhatsApp for web is a platform independent messaging app which allows you to communicate for free.
Mobile messenger app with free voice & video call over 3G/4G & Wi-Fi.
OnionShare lets you securely and anonymously share a file of any size, without any third party involved.
Thunderbird is email and calendar software by Mozilla (the maker of Firefox) that offers the same functionality as the (commercial) office application Microsoft Outlook.