VeraCrypt - VeraCrypt is a free open source disk encryption software for Windows, Mac OSX and Linux.
Folder Lock - Folder Lock is a security software that helps you to password protect files, shred files, clean history, encrypt the personal documents and much more.
Easy File Locker - Easy File Locker is a pretty small file at 224KB and will do exactly what it says.
Wise Folder Hider - Wise Folder Hider is a free file/folder hiding tool.
Axcrypt - AxCrypt - Password Protect Files With Strong Encryption. AxCrypt is the leading open source file encryption software for Windows.
Vov Hide Files - Lock your files and folders from prying eyes.