EmuExec is the right answer to make emulation on linux as simple as possible. But it is more than a simple multisystem frontend, you just have to see it by yourself.
qsh is a shell for any operating system. It is coded in java so it inherits the pros and cons of java. It is in a very nascent stage, but all the regular commands work: Directory navigation, file tasks etc.
PHPterm is a terminal/shell emulator for PHP which let's you execute shell commands just like in a shell, but all within your browser window over the HTTP protocol.
It aims to provide the look and feel of konsole, the KDE terminal.