OnionShare
Open Source
Tor-Powered
OnionShare is an open-source tool that lets you securely and anonymously share a file of any size. It works by starting a web server locally, on your machine, accessible as a Tor Hidden Service, via an unguessable URL.
Notes:
OnionShare is not ran in your browser. Instead, you must download the app. We would also like to note that OnionShare is included with Quebes OS, Tails OS, Whonix, and Parrot OS. It also supports Windows and macOS.
Magic Wormhole
Open Source
Not Anonymous
Magic Wormhole is a linux package that provides a library and a command-line tool named wormhole, which makes it possible to get arbitrary-sized files and directories from one computer to another without prying eyes.
Notes:
For the average user, Magic Wormhole is definitely harder to setup and use, when compared to OnionShare. If you're looking for a simple, easy, and quick solution, we suggest trying OnionShare, however, Magic Wormhole is always an option and can be installed with one command (via snap).