I force all my homies to use magic-wormhole. It can transfer files and folders with no sign-up and (as far as I can tell) no limits.

For all you command-line nerds, including on Windows, it works like this:

> wormhole send <filename>

Sending 0 Bytes file named '<filename>'
Wormhole code is: 1-medusa-puppy
On the other computer, please run:

wormhole receive 1-medusa-puppy

This will ping the relay server, which defaults to Canonical on my system, as I recall, to generate a code so the two computers can locate each other.

Then on the other computer, (again including Windows,)

> wormhole receive 1-medusa-puppy

Waiting for sender...
Receiving file (0 Bytes) into: '<filename>'
ok? (Y/n): y

Receiving (->tcp:192.168.1.1:36587)..
0.00B [00:00, 4B/s]
Received file written to <filename>

Note that, as both computers were on the same LAN, it transferred locally because it's awesome that way.

Working as a TA in the computer science department, this is invaluable. Students from all skill levels can transfer stuff with no extra headache, and the generated codes can be spoken aloud for simplicity.