MonoShell starts with a basic command prompt which asks you for commands. It is not dangerous as it does abseloutely to your hard disk drive. It is simply made for people to have fun.
JaguiD is a Java GUI for DOS. It consists of several sub-projects including a Java Compiler, a Class Runner and a Jar Packager. JaguiD has limited Java support to provide a Graphical User Interface for DOS and compatibles.