Sakai.

Open-source learning management system widely adopted by European universities

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BigBlueButton
Open-source web conferencing system designed specifically for online learning
DE · open-source
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Chamilo
Belgian open-source e-learning and collaboration platform for education and enterprises
BE · open-source
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Classlife
Spanish cloud-based education management platform for schools and universities
ES · commercial
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Open edX
Open-source online learning platform with significant European university deployments
ES · open-source
↗
Forma LMS
Italian open-source learning management system designed for corporate training
IT · open-source
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H5P
Norwegian open-source framework for creating interactive educational content and activities
NO · open-source
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ILIAS
German open-source learning management system used by universities and organisations across Europe
DE · open-source
↗
itslearning
Norwegian cloud-based learning management system for K-12 and higher education
NO · commercial
↗