The best open source alternative to Nextcloud is ownCloud. If that doesn't suit you, our users have ranked more than 100 alternatives to Nextcloud and loads of them is open source so hopefully you can find a suitable replacement. Other interesting open source alternatives to Nextcloud are Ente Photos, Seafile, Filen and Proton Drive.
Syncany is an open-source cloud storage and filesharing application. It allows users to backup and share certain folders of their workstations using any kind of storage, e.g. FTP, Amazon S3 or Google Storage.
All you need in a team collaboration tool dedicated to small efficient teams. Chat, notes, drive, online collaborative edition, calendars, news, spaces, notifications...
e2ee-cloud is a open source, self-hosted, end-to-end encryption software. You can upload and download files in your browser. All files and folders will be encrypted before upload and decrypted after download.
Astian Cloud is a secure and private storage alternative where users can store their information, share files, edit files, video conferences and much more.
A secure and ephemeral way to transmit sensitive information to anyone. Sends can include plaintext or file attachments up to 100 MB.
fruux is a free service that takes care of your contacts, calendars and more so you don't have to. Never manually copy contacts and calenders between your devices again!
Excellent file management and collaboration for public authorities, providers and business - or anyone who values ease of use and digital sovereignty.
Secure, end-to-end encrypted, and privacy respecting sync for your contacts, calendars and tasks. Everything is encrypted on the client-side and all the code (client and server) is open source.
The Amahi Home Server is designed for home and small office environments where the technical support staff do not want the job!
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Very serious, free and open source !