metashell is a lightweight, heavy punch, interactive, intelligent command line shell. The difference lies in its ability to determine a file's data type, and automatically run your desired applications. It uses file data types (MIME types) to determine a file's type, and then using user-defined applications automatically opens the file.
Secure Back Door (SBD) is a tool that provides ultra-secure and minimal access to a computer, which allows you to run a single command based on a one time key. It is good if you don't want to have an SSH server running all the time, and only want to start it when needed. Because it is written in only a few lines of code, it is hoped that it will be less susceptible to security exploits than a program like SSH.