ffsend - Easily and securely share files from the command line. A fully featured Firefox Send client.
Transfer.sh - Easy file sharing from the command line or web.
Syncthing - Open Source Continuous File Synchronization.
OnionShare - Securely and anonymously send and receive files, and publish onion sites.
bita - Differential file synchronization over http.
Filestash - Modern web client for SFTP, S3, FTP, WebDAV, Git, Minio, LDAP, CalDAV, CardDAV, Mysql, Backblaze.