The best open source Cloud Storage alternative to Cryptomator is Cryptsync. If that doesn't suit you, our users have ranked more than 50 alternatives to Cryptomator and five of them are open source Cloud Storage Services so hopefully you can find a suitable replacement. Other interesting open source Cloud Storage Service alternatives to Cryptomator are Internxt Drive, File Lock PEA, Syncany and Rclone GUI.
CryptSync is a small utility that synchronizes two folders while encrypting the contents in one folder. That means one of the two folders has all files unencrypted (the files you work with) and the other folder has all the files encrypted.
Open-source, privacy-focused cloud storage using zero-knowledge encryption and blockchain technology, provides secure file transfer, end-to-end encryption, free 10 GB plan, desktop and mobile support, full user control, and no data tracking or ads.
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.
A GUI for Rclone, with additional features including batch file generation, auto cloud setup, and saved file/folder paths.
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only alternative to Cryptomator, although I dont think you need one. Cryptomator works awesome on Linux!