NextGEN Moodle Integrated Remote Classroom & Web-conferencing BigBlueButton, GoToWebinar, WizIQ and Zoom are web conferencing and virtual classroom systems for online learning. They are "deep integrated" with NextGEN Moodle.
BigBlueButton is opensource and free if you host it yourself. GoToWebinar and WizIQ are subscription based. Zoom has free version, a low cost and a high cost option.