MLCrypt
Simple, lightweight, standalone command-line single file encryption.
Simple, lightweight, cross-platform (Windows / Linux / ARM6 Linux), cross-arch (x32 / x64), standalone command line file encryption program.
GnuPG is probably the best application for cross-platform encryption. However, its usage on Windows PCs may be inconvenient (installation administrator rights; large executable size for perhaps just a one-time file decryption, complicated command-line switches for stronger encryption). NCrypt would fulfill this task, but does not operate on 64-bit Windows - MLCrypt was created because of this.
The program's primary aim is cascade encryption: create an encrypted outer layer over an existing compressed and encrypted archive file. (Each encryption layer should have a different complex password.)
MLCrypt.zip contains all the executables: Linux, Windows, Raspberry Pi.