The corps I've been with use GTM and WebEx for online meetings. It's convenient for sharing your screen with others, especially for a training or tutorial session.
Discord and Skype is more catered for social media; DM, voice chats, video chat, but I don't think it supports screen sharing. Some companies use skype internally to communicate with each other, but when it's a conference call with third-parties, I mainly see GTM or WebEx being used.