VeraCrypt - VeraCrypt is a free open source disk encryption software for Windows, Mac OSX and Linux.
Steghide - Steghide is a steganography program that is able to hide data in various kinds of image- and...
Easy File Locker - Easy File Locker is a pretty small file at 224KB and will do exactly what it says.
OpenPuff - OpenPuff is a professional steganography tool: HW seeded random number generator (CSPRNG)
Axcrypt - AxCrypt - Password Protect Files With Strong Encryption. AxCrypt is the leading open source file encryption software for Windows.
DeepSound - DeepSound is the way of hiding your message in an audio file.