OnionShare lets you securely and anonymously share files of any size. It works by starting a web server, making it accessible as a Tor onion service, and generating an unguessable URL to access and download the files. It doesn't require setting up a server on the internet somewhere or using a third party file-sharing service. You host the file on your own computer and use a Tor onion service to make it temporarily accessible over the internet. The other user just needs to use Tor Browser to download the file from you.
How to Use
Open OnionShare, drag and drop files and folders you wish to share into it, and click Start Sharing. After a moment, it will show you a .onion URL such as
http://asxmi4q6i7pajg2b.onion/egg-cain. This is the secret URL that can be used to download the file you're sharing.
Send this URL to the person you're sending the files to. If the files you're sending aren't secret, you can use normal means of sending the URL, like by emailing it, or sending it in a Facebook or Twitter private message. If you're sending secret files then it's important to send this URL securely.
The person who is receiving the files doesn't need OnionShare. All they need is to open the URL you send them in Tor Browser to be able to download the file.