The best Web Conferencing alternative to MicroSIP is Linphone, which is both free and Open Source. If that doesn't suit you, our users have ranked more than 25 alternatives to MicroSIP and four of them are Web Conferencing Tools so hopefully you can find a suitable replacement. Other interesting Web Conferencing Tool alternatives to MicroSIP are Blink, Tauria and Spreed.
Linphone is one of the most famous open source softphones in the world. It is fully SIP-based, for all calling, presence and IM features.
Fully end-to-end encrypted business collaboration platform that is the only on the market supporting E2EE HD video conference up to 100 participants.
Spreed is the worldwide unified web conferencing service offering integrated web and telephone conferencing. It is based on Flash Player. Free service includes 3 attendees and max 1.5h meetings. Single events or monthly service can be purchased.
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Linphone has a far worse UI and has no way to, for example, set up an SIP account with a proxy server.