Syncany - Syncany is an open-source cloud storage and filesharing application.
Beyond Compare - Beyond Compare allows you to compare files and folders.
Filestash - Filestash is a modern client for FTP, SFTP, S3, WebDAV, Minio,...
WinMerge - WinMerge is an open source differencing and merging tool for Windows.
Dropbox - Online Sync and File Sharing
Meld - What is Meld? Meld is a visual diff and merge tool targeted at developers.