Onionshare - OnionShare lets you securely and anonymously share a file of any size with someone.
VeraCrypt - VeraCrypt is a free open source disk encryption software for Windows, Mac OSX and Linux.
ShareDrop - HTML5 clone of Apple's AirDrop - easy P2P file transfer powered by WebRTC
Axcrypt - AxCrypt - Password Protect Files With Strong Encryption. AxCrypt is the leading open source file encryption software for Windows.
Send Anywhere - Send whatever you want, wherever you want
Windows BitLocker - This topic provides a high-level overview of BitLocker, including a list of system requirements, practical applications, and deprecated features.