What open-source alternatives to Zoom exist for teaching?

Three open-source projects come up most often for live teaching. All run in the browser and can be self-hosted or used through a hosting provider.

BigBlueButton (licence: LGPL v3) was designed specifically for online classes. It includes a multi-user whiteboard, presentation upload, breakout rooms, polls, shared notes, recordings and moderator controls, and it has long-standing integrations with Moodle, Chamilo and other learning platforms. It needs a dedicated, fairly powerful server and is opinionated about how it is installed.

plugNmeet (licence: MIT) is a newer platform built on the LiveKit media server. It offers similar teaching tools (whiteboard, breakout rooms, polls, recordings) plus MP4 recordings, live streaming to YouTube or Facebook, optional end-to-end encryption and AI features such as live captions and translation. It provides a BigBlueButton-compatible API and LTI, so it can replace BigBlueButton in many existing integrations. Disclosure: plugNmeet is maintained by MynaParrot.

Jitsi Meet (licence: Apache 2.0) is a general video conferencing tool. It is quick to start, works well for meetings and small groups, and is easy to embed in other apps. It has fewer classroom-specific tools than the other two, so it is often used for tutoring or meetings rather than full courses.

How to choose: list the features you actually use in class, check how the tool connects to your learning platform, and run a test with a realistic number of participants. Licence matters too: MIT and Apache 2.0 are permissive; LGPL has some obligations if you modify and distribute the software.