Microsoft SharePoint is not available as a self-hosted solution but there are plenty of alternatives for power users and business that want to host a solution on-premise. The best Self-Hosted alternative is Nextcloud, which is both free and Open Source. If that doesn't suit you, our users have ranked more than 100 alternatives to Microsoft SharePoint and many of them are available as a self-hosted solution so hopefully you can find a suitable replacement. Other interesting Self-Hosted alternatives to Microsoft SharePoint are ownCloud (Freemium, Open Source), MediaWiki (Free, Open Source), XWiki (Free, Open Source) and Confluence (Paid).
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MediaWiki is a free software wiki package written in PHP, originally for use on Wikipedia. It is now used by several other projects of the non-profit Wikimedia Foundation and by many other wikis, including this website, the home of MediaWiki.
MediaWiki vs Microsoft SharePoint opinions
pros, cons and recent comments
SharePoint is a cloud/file sharing server whereas MediaWiki is just for the WikiMedia projects and isn't even a cloud/storage server.
Foam is a personal knowledge management and sharing system inspired by Roam Research, built on Visual Studio Code and GitHub. You can use Foam for organising your research, keeping re-discoverable notes, writing long-form content and, optionally, publishing it to the web.
eXo Platform is an all-in-one digital workplace solution that helps you connect, align and engage your teams around a single interface. You can use it to improve company and peer-to-peer communication, boost collaboration and manage company knowledge.