Skype is a proprietary telecommunications application that specializes in providing video chat and voice calls between computers, tablets, mobile devices, the Xbox One console, and smartwatches over the Internet.
Google Hangouts is a unified communications service that allows members to initiate and participate in text, voice or video chats, either one-on-one or in a group.
Hypothesis is a free online tool designed to allow for collaborative annotation across the web. It can be used to annotate web pages, pdfs, and EPUB files. You can annotate documents and pages publicly, privately, or within a group.
Web conferencing is used as an umbrella term for various types of online conferencing and collaborative services including webinars, webcasts, and web meetings.
