Zoom (https://illinois.zoom.us) is an online audio- and video-conferencing service. You can use Zoom to share (and record) audio and video for one-to-many lectures, or to hold live chat or audio discussions. It has software for Windows, Mac, and Linux as well as iOS and Android apps for mobile users.
Skype for Business is a Microsoft application that runs on Windows and Mac, as well as Android and iOS-based mobile devices. When you’re off-campus, you can use Skype for Business to make and receive phone calls from your office phone number – if you use a computer, you’ll just need a microphone and speakers or headphones (preferably ones with a microphone). Skype for Business can also be used for audio and video conferencing. It is not as simple as Zoom, but may be a good alternative if the Zoom network is overloaded. Undergrads (who do not receive Skype for Business accounts) can join a “meeting” (i.e. one-to-many lecture) through the web client. Students with regular Skype accounts can join meetings with full audio, video, and chat capabilities.
Box (https://uofi.app.box.com) is a file-sharing service. It can be used to make files available to your students, such as a PDF of a PowerPoint presentation. We suggest making your links open to “Anyone with the link” (see https://answers.illinois.edu/75695 for more information), so that students do not need to log in to get to instructional content.